Switching from MG 180CMJ to MG 180JHP

[tackdr1ver]

I am considering trying out the MG 180 JHP's. I have been running the MG 180 CMJ's without issue but curiosity is getting the best of me. I am wondering where I should start?

Mainly the questions I have are in relation to seating and charge.

Current load is: 180 Gr MG CMJ

1.180 OAL

5.3gr VVn320

Fed no 100 primer

When switching from the CMJ to the JHP what should I expect if I seat to same OAL with the same charge? Is pressure going to spike or drop? I would guess that it will spike as I think the 180 JHP is a bit longer to make up for the hollow point??

Edited October 28, 2012 by tackdr1ver

[Youngeyes]

IMHO: CMJ or JHP same,same. Look here for other opinions.

http://www.brianenos.com/forums/index.php?showtopic=136143

[rangerguy]

If it ain't broke don't fix it.

[tackdr1ver]

If it ain't broke don't fix it.

true man, true.

[CHA-LEE]

The JHP's will be longer than the CMJ's. Since the JHP's are longer they consume more case volume if you seat them to the same OAL dept as the CMJ's. Less case volume creates more pressure and more velocity. If you keep the same OAL you should lower the powder drop at least 0.5gr to start a little low then work your way back up to the same velocity as the CMJ's one tenth of a grain at a time. Alternately you can keep the same powder drop but increase the OAL, but you may run into feeding issues by changing the length of the round. If your current OAL feeds properly then I would suggest leaving it the same and change the powder drop to match what is needed.

[noylj]

CHA-LEE:

you are confusing seating depth (in the case) with COL (cartridge overall length). If the JHP is seated to the same COL, there could be less bullet seated in the case. Depends on comparative bullet lengths.

The thing to understand is that ANY change in bullet means going back to starting load and working up a NEW COL. Even two different FMJ-RN bullets are unlikely to be so dimensionally identical that the same COL is best for both.

New reloaders seem not to understand the COL is as GUN dependent as it is bullet dependent.

Variables that effect the COL that will feed and chamber reliably depends on:

Bullet ogive and meplat

Magazine lips (when in the feeding cycle the round is released)

Feed ramp geometry

Chamber dimensions

Thus, a change from a 1R to a 2R round nose can significantly change the best COL.

[Steve RA]

The "plunk" test is your friend !!

[Ssanders224]

The JHP's will be longer than the CMJ's. Since the JHP's are longer they consume more case volume if you seat them to the same OAL dept as the CMJ's. Less case volume creates more pressure and more velocity. If you keep the same OAL you should lower the powder drop at least 0.5gr to start a little low then work your way back up to the same velocity as the CMJ's one tenth of a grain at a time. Alternately you can keep the same powder drop but increase the OAL, but you may run into feeding issues by changing the length of the round. If your current OAL feeds properly then I would suggest leaving it the same and change the powder drop to match what is needed.

I think this^^ is a pretty good recommendation.

CHA-LEE: you are confusing seating depth (in the case) with COL (cartridge overall length). If the JHP is seated to the same COL, there could be less bullet seated in the case. Depends on comparative bullet lengths.The thing to understand is that ANY change in bullet means going back to starting load and working up a NEW COL. Even two different FMJ-RN bullets are unlikely to be so dimensionally identical that the same COL is best for both.New reloaders seem not to understand the COL is as GUN dependent as it is bullet dependent.Variables that effect the COL that will feed and chamber reliably depends on:Bullet ogive and meplatMagazine lips (when in the feeding cycle the round is released)Feed ramp geometryChamber dimensionsThus, a change from a 1R to a 2R round nose can significantly change the best COL.

I dont see what CHA-LEE is confusing? He stated that the JHPs are longer, therefore if seated to the same OAL/COL as the FMJ, the case volume will be less and pressures will be higher given the powder charge stays the same.

Makes sense to me.

Plus he took into account that OAL is "GUN dependent", suggesting that if the OPs current OAL cycles well, then mimick the length with the JHPs and back off the powder charge.

[noylj]

I give up. I guess my JHPs are different.

[FightFireJay]

I give up. I guess my JHPs are different.

if they have the same profile, a jhp HAS to be longer. But if the profile is different (or a different material, like lead free) then you could have an FMJ or TMJ be longer than equivalent JHP.

[Justsomeguy]

On another note, though this does not apply in this case since the BRAND and construction of the two bullets is similar, changing bullet BRANDS can raise or lower pressures because of the difference in hardness of the jacket alloy and the "slippery-ness" of the bullet. So if you change brands whether or not it is the same bullet design, you should still go back to square one and work the load up again. But yes, the change in bullet TYPE here, even from the same manufacturer, will take a chrono session or two to verify what OAL you might want to run with.

[ninemmbill]

Safest option is starting over to develop a new load. Determine your overall length and then using a chrono, work up the powder charge until you get the desired velocity, function, or power factor results.

[gordonm1]

+1 to ninemmbill's comments.

I don't know the differences between montanna gold bullets between hp and CMJ but one observation I have made is in 45 ACP, even though the 230gr HP has a shorter nose than 230 RN, it has to be loaded to a shorter OAL to keep it off the lands of my barrel. Much 230 gr JHP is loaded at 1.200" and 230 RN 1.235" to 1.26". Loads are diiferent for them in manuals too usually. Different case volume is probably why.

You may experience the opposite with you switch of bullets so staring over is a safe idea.