CMJ vs. JHP reliability

[TwoShot]

I have shot over 10,000 MG 125 CMJ's through my 9mm STI Trubor without any feeding issues. The accuracy is less than I expect with this bullet. As I am improving my shooting, I guess I expect more from the gun. I have heard many on the forum suggest that JHP's are more accurate. I am using STI mags with spacers loading to an oal of 1.160 as per H. Smith, B. Grams and B. Keigans. What can I expect if I switch to MG 125 JHP's as far as accuracy and reliability? Yes, I searched!

Edited April 21, 2010 by TwoShot

[lcs]

The accuracy is less than I expect with this bullet. As I am improving my shooting, I guess I expect more from the gun.

What accuracy limitations are you experiencing?

At a high level view--Your "improving" should not have any effect (good or bad) on how accurate the gun is. The gun and load is what it is.

In our world of shooting--The accuracy of CMJ versus a JHP is somewhat moot.

[BMartens]

I have compared the MG 124 CMJ and JHP and her is what I found.

Accuracy - Slight edge to the JHP at 25 yards. Just enough to notice.

Reliability - Exactly the same, zero issues with either @ 1.150 OAL

Biggest difference for me was I can get more velocity with the JHP. Runs about 3-4 points higher for PF. Was pushing a couple of loads to make 170 PF and with the JHP I got there with no problems and even backed off .1 or .2 grains on a couple of loads.

SV mags, no spacers, Grams intenals and Dawson base pads.

Edited April 21, 2010 by BMartens

[G-ManBart]

[quote name='BMartens' date='21 April 2010 - 02:01 PM' timestamp='1271872865' =Biggest difference for me was I can get more velocity with the JHP. Runs about 3-4 points higher for PF. Was pushing a couple of loads to make 170 PF and with the JHP I got there with no problems and even backed off .1 or .2 grains on a couple of loads.

That's because at the same OAL, the JHP's take up more case volume, which raises the pressure and velocity. R,

Edit to add: both of my current Open guns (.38SC) seem to feed MG 121gr IFP, MG 115gr JHP, MG 115gr CMJ and Zero 125gr JHPs equally well...perfectly. For a gun that's even slightly picky, I'd go with the CMJ's assuming your gun shoots them well enough, which is very likely. I'd be surprised to find that someone got great accuracy with an MG 115 JHP and mediocre accuracy with an MG 115gr CMJ.

Edited April 21, 2010 by G-ManBart

[kgunz11]

I agree, the difference in accuracy should be moot. I have found the profile of the CMJ to be more favorable for reliable feeding. Not that there is anything wrong with the JHP, but it's flat nose cannot be as favorable feeding as the pointed nose of the CMJ. Does that mean anyone will ever have a problem with the JHP? No, but there is less chance of it happening with a CMJ. Susan's gun shot a 5 shot ragged hole the other day at the range at 20 yards when checking her C-More with CMJ's. I thought I was missing the head of the target and walked up to check it out. She saw it and started laughing because I thought I was missing.

My vote for a 9mm S_I still favors the CMJ, no matter what mags and what level of tuning is done on them. The geometry of the CMJ speaks for itself.

[steel1212]

With my 9mm SS the CMJs feed much better than the JHP. MG's JHP have a very square profile. I have not tried Zeros yet, and they have a more rounded profile.

[Jaxshooter]

I am currently shooting the MG 121 IFP loaded to 1.160. Prior load was Zero 125gr JHP same length. Never had any type of problem with these loads in 3 different 9MM Major Open guns. Prior to going to 9mm I used the 125gr Zero JHP in a 38SC open gun with no problems.

[BMartens]

The MG CMJ's run .596 and the JHP averages .582 so the case volume is greater, not less, for the JHP at the same OAL. I think the increase in velocity is due to the bullet profile with much more bearing surface for the JHP. In essence, the result is the same, a little more pressure.

I also agree the CMJ sure looks like it would feed better but, I have not had a single feeding problem with 124 CMJ/JHP, 115 JHP, Zero or MG, so that is just not a factor for me.

Accuracy for all of the bullets mentioned has been excellent, between 1.3" and 1.7". The other thing that seems a bit odd is that all of them shoot to almost the same POI for the different loads.

[TwoShot]

Thanks to all for the reply's and sharing your experiences. To explain my comment about expecting more from the gun. When I started this game, if I had to shoot a partially exposed target, I shot for the center of the exposed area. As I improve and have greater confidence, I shoot for the smaller A zone, that is closer to the no-shoot or hard cover, as the case may be. That said, I'm going to stick with CMJ's, reliability is paramount to me in this game.

[G-ManBart]

The MG CMJ's run .596 and the JHP averages .582 so the case volume is greater, not less, for the JHP at the same OAL. I think the increase in velocity is due to the bullet profile with much more bearing surface for the JHP. In essence, the result is the same, a little more pressure.

I also agree the CMJ sure looks like it would feed better but, I have not had a single feeding problem with 124 CMJ/JHP, 115 JHP, Zero or MG, so that is just not a factor for me.

Accuracy for all of the bullets mentioned has been excellent, between 1.3" and 1.7". The other thing that seems a bit odd is that all of them shoot to almost the same POI for the different loads.

It's the profile of the bullet, not the total length of the bullet, that dictates OAL. At the same OAL, JHPs are almost always taking up more case volume than an FMJ of the same weight. No need to trust me...just load one of each to the same oal and look at where the base of the bullet is and it'll be very obvious. Bearing surface makes so little difference in this sort of application (and most others really) that you probably couldn't measure it with a chronograph and hundred round strings.

I haven't used any of MG's 124gr bullets, but both 115s and the 121s fed perfectly in both of my Open guns as well...non-factor.

[BMartens]

The MG CMJ's run .596 and the JHP averages .582 so the case volume is greater, not less, for the JHP at the same OAL. I think the increase in velocity is due to the bullet profile with much more bearing surface for the JHP. In essence, the result is the same, a little more pressure.

I also agree the CMJ sure looks like it would feed better but, I have not had a single feeding problem with 124 CMJ/JHP, 115 JHP, Zero or MG, so that is just not a factor for me.

Accuracy for all of the bullets mentioned has been excellent, between 1.3" and 1.7". The other thing that seems a bit odd is that all of them shoot to almost the same POI for the different loads.

It's the profile of the bullet, not the total length of the bullet, that dictates OAL. At the same OAL, JHPs are almost always taking up more case volume than an FMJ of the same weight. No need to trust me...just load one of each to the same oal and look at where the base of the bullet is and it'll be very obvious. Bearing surface makes so little difference in this sort of application (and most others really) that you probably couldn't measure it with a chronograph and hundred round strings.

I haven't used any of MG's 124gr bullets, but both 115s and the 121s fed perfectly in both of my Open guns as well...non-factor.

Sorry but, simple math rules in this instance. We all measure OAL the same way, from the base of the case to the tip of the bullet, regardless of bullet profile. We measure bullet length from the base of the bullet to the tip. When measured from the same reference point, the bullet tip, the shorter bullet will leave more space in the case.

Draw two parallel lines 1.150" apart. Draw a perpendicular line descending from the top line that is .596" long. Draw another line in like fashion that is .582" long. If the bottom of each descending line represents the base of the bullet I do believe the longer bullet will seat deeper in the case resulting in less case volume.

Bearing surface and bullet/jacket material do make a significant difference in our application.

[TerryO]

OK, along these lines, I've shot MG 124gr CMJ and Zero 121gr JHP in my guns. Both run flawlessly. I like the profile of the 121gr better than the MG but MG is easier to get. So my question is does anyone have opinions on Zero 121 JHP vs MG 121 IFP since that's another 121gr option?

[G-ManBart]

The MG CMJ's run .596 and the JHP averages .582 so the case volume is greater, not less, for the JHP at the same OAL. I think the increase in velocity is due to the bullet profile with much more bearing surface for the JHP. In essence, the result is the same, a little more pressure.

I also agree the CMJ sure looks like it would feed better but, I have not had a single feeding problem with 124 CMJ/JHP, 115 JHP, Zero or MG, so that is just not a factor for me.

Accuracy for all of the bullets mentioned has been excellent, between 1.3" and 1.7". The other thing that seems a bit odd is that all of them shoot to almost the same POI for the different loads.

It's the profile of the bullet, not the total length of the bullet, that dictates OAL. At the same OAL, JHPs are almost always taking up more case volume than an FMJ of the same weight. No need to trust me...just load one of each to the same oal and look at where the base of the bullet is and it'll be very obvious. Bearing surface makes so little difference in this sort of application (and most others really) that you probably couldn't measure it with a chronograph and hundred round strings.

I haven't used any of MG's 124gr bullets, but both 115s and the 121s fed perfectly in both of my Open guns as well...non-factor.

Sorry but, simple math rules in this instance. We all measure OAL the same way, from the base of the case to the tip of the bullet, regardless of bullet profile. We measure bullet length from the base of the bullet to the tip. When measured from the same reference point, the bullet tip, the shorter bullet will leave more space in the case.

Draw two parallel lines 1.150" apart. Draw a perpendicular line descending from the top line that is .596" long. Draw another line in like fashion that is .582" long. If the bottom of each descending line represents the base of the bullet I do believe the longer bullet will seat deeper in the case resulting in less case volume.

Bearing surface and bullet/jacket material do make a significant difference in our application.

Again, don't trust me, don't try using math...go seat a JHP and and FMJ to the same OAL and see where the base is. The JHP will normally be using more case volume (obviously varies with different profiles) and that is the reason why you're getting a higher velocity. Less case volume, more pressure, higher velocity...

A couple thousandths of an inch difference in bearing surface means zippy. Again, go try the two and you'll see for yourself. R,

Edited April 22, 2010 by G-ManBart

[High Lord Gomer]

I don't load CMJs and JHPs at the same OAL. For my M&Ps, I run 115gr CMJs at 1.125 and 115gr JHPs at 1.087. If the JHP is shorter by .014 and I load it to an OAL that is .038 less, I have seated it .024 deeper than the CMJ.

I get significantly higher speeds out of the JHPs.

[njl]

Yep, simple math....except we don't seat the bullet off the tip of the nose, so it becomes complex math. The seating stem makes contact at different points on bullet based on the shape, and that causes the difference, not the total length of the bullet

Again, don't trust me, don't try using math...go seat a JHP and and FMJ to the same OAL and see where the base is. The JHP will be using more case volume and that is 100% the reason why you're getting a higher velocity. Less case volume, more pressure, higher velocity...

A couple thousandths of an inch difference in bearing surface means zippy. Again, go try the two and you'll see for yourself. R,

In the case of MG 124gr CMJ and MG 124gr JHP, the JHP bullets are actually about 0.02" shorter, so at the same COAL, you actually have more case volume with the JHP. I think most people load the JHP to a shorter COAL than the CMJ. Even adjusting COAL to keep the volume about the same, the JHP seem to run a little faster.

[BMartens]

The MG CMJ's run .596 and the JHP averages .582 so the case volume is greater, not less, for the JHP at the same OAL. I think the increase in velocity is due to the bullet profile with much more bearing surface for the JHP. In essence, the result is the same, a little more pressure.

I also agree the CMJ sure looks like it would feed better but, I have not had a single feeding problem with 124 CMJ/JHP, 115 JHP, Zero or MG, so that is just not a factor for me.

Accuracy for all of the bullets mentioned has been excellent, between 1.3" and 1.7". The other thing that seems a bit odd is that all of them shoot to almost the same POI for the different loads.

It's the profile of the bullet, not the total length of the bullet, that dictates OAL. At the same OAL, JHPs are almost always taking up more case volume than an FMJ of the same weight. No need to trust me...just load one of each to the same oal and look at where the base of the bullet is and it'll be very obvious. Bearing surface makes so little difference in this sort of application (and most others really) that you probably couldn't measure it with a chronograph and hundred round strings.

I haven't used any of MG's 124gr bullets, but both 115s and the 121s fed perfectly in both of my Open guns as well...non-factor.

Sorry but, simple math rules in this instance. We all measure OAL the same way, from the base of the case to the tip of the bullet, regardless of bullet profile. We measure bullet length from the base of the bullet to the tip. When measured from the same reference point, the bullet tip, the shorter bullet will leave more space in the case.

Draw two parallel lines 1.150" apart. Draw a perpendicular line descending from the top line that is .596" long. Draw another line in like fashion that is .582" long. If the bottom of each descending line represents the base of the bullet I do believe the longer bullet will seat deeper in the case resulting in less case volume.

Bearing surface and bullet/jacket material do make a significant difference in our application.

Again, don't trust me, don't try using math...go seat a JHP and and FMJ to the same OAL and see where the base is. The JHP will normally be using more case volume (obviously varies with different profiles) and that is the reason why you're getting a higher velocity. Less case volume, more pressure, higher velocity...

A couple thousandths of an inch difference in bearing surface means zippy. Again, go try the two and you'll see for yourself. R,

You didn't draw those pesky little lines, did you?

[njl]

You didn't draw those pesky little lines, did you?

I wonder if we're talking about different things. Without adjusting the seating die, seating different shape bullets can result in different COALs.

If you have bullets that are 0.600" long and 0.580" long, and seat each to a measured COAL of 1.150, then it should be obvious to all that the cartridge with the shorter bullet has more case volume (0.02 * Pi * r^2 more...ignoring any case tapering, differences in the two pieces of brass, etc.).

[kgunz11]

You didn't draw those pesky little lines, did you?

I wonder if we're talking about different things. Without adjusting the seating die, seating different shape bullets can result in different COALs.

If you have bullets that are 0.600" long and 0.580" long, and seat each to a measured COAL of 1.150, then it should be obvious to all that the cartridge with the shorter bullet has more case volume (0.02 * Pi * r^2 more...ignoring any case tapering, differences in the two pieces of brass, etc.).

No Sir, not necessarily, not if the seating stem contacts the bullet in a different place. The stem is what contacts the bullet, aligns it, and pushes it down in the case. The shape of the bullet effects when and where the stem contacts the bullet.

Bart is correct in theory, but in this application I do not know if it proves true. I wouldn't bet against him though, I'm sure he's done his homework.

A long pointed bullet may take exactly the same amount of space in the case as a short fat bullet of equal weight according to the ogive engagement of the 2 bullets.

[njl]

You guys either aren't reading or have issues with spatial relationships.

Two cartridges (same caliber...we are talking about different 9mm bullets here) are loaded with different length bullets.

Each cartridge has been loaded to the same COAL. i.e. calipers on each cartridge say they are each 1.140" long just to pick a number.

We're assuming that because we're talking about CMJ vs JHP, that both bullets have flat bases that don't add to the case volume.

The cartridge with the longer bullet has less case volume because more of the bullet's length is inside the case.

The shape of the ogive is irrelevant. Where the seating stem contacts the bullet is irrelevant. The seating die has been properly adjusted for each bullet to seat them to a COAL of 1.140".

[G-ManBart]

It depends on the exact bullets in question. I'm sure it's not a universal rule, but in many cases the JHPs take more case volume at the same OAL. I'll try to post some pics tonight with one of each seated to the same OAL.

While it's not 9mm, I had a .40 load with 180gr FMJ's in Win cases and 180 JHPs in Starline cases. They gave me identical power factors. The SL cases had a couple of grains more case volume to start with and that evened things out since the JHP took up more case volume. If I put the JHPs in the Win cases my PF jumped considerably. If I put the FMJs in the SL cases my PF dropped considerably. It was all directly related to case volume used and predictable. R,

[kgunz11]

MG JHP 0.578"

MG CMJ 0.588"

Not touching the seating die, the JHP COAL is 1.138" and the CMJ is 1.176" COAL.

JHP has .400" out of the case.

CMJ has .430" out of the case.

Now pull out your calculators and figure the difference.

[BMartens]

A cartridge OAL of 1.150" is exactly what it says. It is not measured from a reference point on the ogive, it is simply measured from the base of the case to the tip of the bullet.

Same thing with the bullets in question, from the base of the bullet to the tip. The MG CMJ bullet is longer than the MG JHP bullet. That only pertains to these bullets, other bullets, other profiles, the JHP might be longer but, not in the case of the MG CMJ and MG JHP.

If you do not adjust your seating die and just change bullets you will not get an OAL of the same value unless the bullets have exactly the same profile. That's why that little seating depth adjustment thing is on there.

[BMartens]

You guys either aren't reading or have issues with spatial relationships.

Two cartridges (same caliber...we are talking about different 9mm bullets here) are loaded with different length bullets.

Each cartridge has been loaded to the same COAL. i.e. calipers on each cartridge say they are each 1.140" long just to pick a number.

We're assuming that because we're talking about CMJ vs JHP, that both bullets have flat bases that don't add to the case volume.

The cartridge with the longer bullet has less case volume because more of the bullet's length is inside the case.

The shape of the ogive is irrelevant. Where the seating stem contacts the bullet is irrelevant. The seating die has been properly adjusted for each bullet to seat them to a COAL of 1.140".

Amen.

[kgunz11]

OK, chew on this. If the MG CMJ is .010" longer when seated at the exact same COAL it will be 0.010" deeper in the case taking up more volume than the MG JHP. Fair enough?

[BMartens]

OK, chew on this. If the MG CMJ is .010" longer when seated at the exact same COAL it will be 0.010" deeper in the case taking up more volume than the MG JHP. Fair enough?

Amen.