PF too high for a STI Trubor 38SC ?

[timothy]

Hi, I bought a 38 super STI Trubor (5" barrel open gun with T2 style Compensator; no popple holes) from the original owner earlier this year.  It's my first open gun.  I have owned an SVI limited 40 that I have reloaded for the past 20 years.  In my quest for the right load recipe for the Trubor I looked thru posts on this forum as well as the Jeff Maas .38 Super IPSC Loads List.

 

I tried many different bullet type/weight vs Powder charge (all HS6 given that this is popular for compensated guns and readily available) to get something that works for that gun, meaning is accurate and minimizes muzzle flip.  For reference I have attached PDF of notes, which reflects some of my testing.

 

So I arrived at the following for a load recipe:

Zero 115 JHP .355 Dia,

Hodgdon HS6 9.5gn,

COL 1.246

This provides a velocity of about 1550FPS which works out to a Power Factor of 178.

 

I was speaking with a shooting friend today who owns several open guns and he feels that with this recipe/178 PF I am taking a significant chance of cracking the slide within a few years and I should reduce the load.

 

So here's my question, I am interested to hear any constructive feedback on whether this is likely to happen.  I'm reluctant to alter this load absent additional compelling data/input.  My sense is that this gun/comp combination requires a high volume of powder to work the comp and my own testing indicates less accuracy/consistency with a smaller powder charge. I also have the impression (from above cited sources) that although 178 is obviously > 165, that it's not out of the stratosphere.  Of course I could be wrong and need to keep an open mind.  Hence this post.  I'm particularly interested to hear from others with the same or similar gun.

Chronodata STI Trubor 38 Super 20220507 and accuracy notes.pdf

[zzt]

If 178 with HS-6 makes the gun shoot as flat as you want, but you are concerned about longevity, go with a slower powder.  You are not case capacity limited with 38S, so try 3N38, SWMP or AA7.  All are superior to HS-6.  Most 38S shooters love 3N38.  SWMP and AA7 are slower, so you use more.  More powder makes more gas.  More gas makes the comp and poppels work better.  Slower powders equal less pressure for the same PF.  You will have to retune your gun to the new load, but chances are you will be softer and flatter with a PF a lot lower than 178.

 

I think you should examine the barrel and comp area.  Your groups are crappy.  If you can't put all the shots into the same hole at 14 yards, or in a 1" circle at 25, something is wrong somewhere.  Zero bullets are the second best I've tried.  They are very slightly behind Hornady HAPs.  Montana Gold would be third.  Everglades are nowhere close.

[GigG]

Just for the record.  178PF alone isn't going to crack the frame.  175 used to be the floor of major PF and I along with countless others shot .38 Super for many, many years at 176 - 180 or more.

[CHA-LEE]

Open guns are always on "Borrowed Time" from a perspective of things breaking. You are on the correct path for tuning the load to optimize the recoil & dot tacking. With an Open gun, the Comp needs gas to do its job. As others have already pointed out, slower powders will usually produce more gas at slower projectile velocities.

 

Most Open gun slides crack due to insane slide velocity while cycling. Lighter weight bullets, such as 115gr, will generate much faster slide velocity than heavier bullets like 124gr when pushed at speeds fast enough to make Major AND produce enough Gas to run the comp. The other factor to consider is that Open gun slides are usually lightened significantly which also promotes faster slide velocities. Its all a balancing act. You need a slide light enough that it doesn't cause muzzle dip when it snaps back forward, and you need a bullet weight / comp gas setup aggressive enough to take advantage of it. Going to extreme in either of these scenarios WILL lead to premature failure of something.

 

That being said, Open guns are truly RACE guns. "RACE" anything is setup in a manner which puts performance above longevity. When something is setup for maximum performance its not going to last forever. If you want a gun that lasts forever, then an Open gun isn't what you want.

[timothy]

Thanks for the replies so far.

 

I'm not likely to switch powders anytime soon as I have over 5 lbs of it now.  I was reluctant to try the VV given its price and my perception that it typically is less readily available.  Maybe I'll give it a try after my powder supply has dwindled.  Mainly I wanted feedback on the 178PF concern.  Hopefully more chime in.

 

ZZT, thanks for the detailed input.  One thing you wrote that intrigues me is " If you can't put all the shots into the same hole at 14 yards, or in a 1" circle at 25, something is wrong somewhere....".  You can regularly get a 1" or better group at 25 yards with an open gun?  Really ?  I'm not sure I can get that with a 22 target pistol.  If you can then I guess you're right, something is wrong, and I want to fix it.  What should I be looking for with the barrel and comp?  A buildup in the comp? What else/what other things should I look for?

 

I am very interested to hear from others what they can get out of their open guns for a group of 5 shots at 25 yds, either offhand or bench (not ransom rest).  Most shooters I encounter don't seem to try to establish a group size at this distance, but maybe that observation isn't applicable on this forum.  Either way I'd like to hear from anyone that has established a group size at 25 yds, please. What do you get?

 

[CHA-LEE]

2 hours ago, timothy said:

Thanks for the replies so far.

 

I'm not likely to switch powders anytime soon as I have over 5 lbs of it now.  I was reluctant to try the VV given its price and my perception that it typically is less readily available.  Maybe I'll give it a try after my powder supply has dwindled.  Mainly I wanted feedback on the 178PF concern.  Hopefully more chime in.

 

ZZT, thanks for the detailed input.  One thing you wrote that intrigues me is " If you can't put all the shots into the same hole at 14 yards, or in a 1" circle at 25, something is wrong somewhere....".  You can regularly get a 1" or better group at 25 yards with an open gun?  Really ?  I'm not sure I can get that with a 22 target pistol.  If you can then I guess you're right, something is wrong, and I want to fix it.  What should I be looking for with the barrel and comp?  A buildup in the comp? What else/what other things should I look for?

 

I am very interested to hear from others what they can get out of their open guns for a group of 5 shots at 25 yds, either offhand or bench (not ransom rest).  Most shooters I encounter don't seem to try to establish a group size at this distance, but maybe that observation isn't applicable on this forum.  Either way I'd like to hear from anyone that has established a group size at 25 yds, please. What do you get?

 

 

There is Marksmanship, and then there is Mechanical Accuracy. I can only assume that ZZT's recommended group sizes are based on Mechanical Accuracy as there are not may people that have both the Mechanical Accuracy AND Marksmanship skills to shoot a 1 inch group from and unsupported shooting position at 25 yards. Can it be done? Absolutely. Is that a reasonable expectation from an "Average Skilled Practical Shooter"? Absolutely NOT.

 

If the gun is built right and the ammo is also loaded properly, shooting a 1 inch group at 25 yards from a SUPPORTED position is a good standard to strive for. From a Marksmanship perspective, if you can shoot a 1 inch group consistently at 10 yards UNSUPPORTED then that is sufficient marksmanship skill to hit ANY target you will ever see in a USPSA/IPSC match. I have trained hundreds of practical shooting students over the years and only a handful could consistently shoot a 1 inch group at 10 yards unsupported on demand.

 

So its very important to separate Marksmanship requirements from Mechanical Accuracy requirements as they are two completely different things.

Edited August 10, 2022 by CHA-LEE

[zzt]

14 hours ago, timothy said:

One thing you wrote that intrigues me is " If you can't put all the shots into the same hole at 14 yards, or in a 1" circle at 25, something is wrong somewhere....".  You can regularly get a 1" or better group at 25 yards with an open gun?  Really ?  I'm not sure I can get that with a 22 target pistol.  If you can then I guess you're right, something is wrong, and I want to fix it.  What should I be looking for with the barrel and comp?  A buildup in the comp? What else/what other things should I look for?

 

The first thing I thought of was comp strikes.  So yes, check the comp for buildup and crud.  Same for the barrel.  HS-6 is just plain dirty.  It may be hard to see, but check the crown on the barrel.  Check for leading or copper fouling.  Clean everything super well, then align ream it just in case.

 

The next thing I would do is slug your barrel.  38S barrels are nominally .356" dia.  STI probably used the same blanks for 9mm and 38S, but it pays to check.  If your barrel is .356", then .355" bullets are not a good idea.  You might even try some 124gr .356" HAPs just for fun.

 

Next, check the lockup, or have a gunsmith do it.  If you are not locking up tighter than a drum, you'll never get accuracy.

 

Then check your dot.  That can easily be the culprit.  Once, on my super accurate 45 bullseye gun groups opened up to 6" @ 25, mostly laterally.  Turns out the tension on the windage adjustment screw was lost, and the diode never settled in the same place.  Returned to factory.  Put the replacement on and bingo, return to accuracy.  BTW, the Marvel Unit One is shoot bullseye with came with a sub-.500" group at 50 yards guarantee.  The target the sent with the gun was .443" with Eley Target ammo.  We have a Ransom rest at the club.  So they didn't fib.

 

You are reluctant to change powders.  I get that.  IMO, HS-6 sucks.  At least try a pound of something slower.  The TC2 is a very efficient comp.  No amount of powder I can get to stay in a 9mm case will overwork it.  You have a lot more case capacity, so make use of it.

 

14 hours ago, CHA-LEE said:

I can only assume that ZZT's recommended group sizes are based on Mechanical Accuracy as there are not may people that have both the Mechanical Accuracy AND Marksmanship skills to shoot a 1 inch group from and unsupported shooting position at 25 yards.

 

I never said it was unsupported.  If I could do that, I'd be HM in bullseye.  Imagine.  10 Xs on every string in Timed and Rapid.  Wouldn't that be something.

[CHA-LEE]

ZZT> You never said "Supported" either. Context is important and without it leads to confusion. The OP's response is a prefect example of being confused about your suggested group size at 25 yards.

[rowdyb]

5lbs of powder is $130?? Sell it and get what has been recommended. To balk at a 130 dollar fix in Open is penny wise and pound foolish.

 

And as someone who has also probably had close to a 1000 students in pistol classes over the years very, very few can shoot a 1" group of 5 shots at ten yards when I first assess them. Sorry if I drove this off topic.. 

[timothy]

I went ahead and ordered some AA #7 and some 3N38.  Hopefully my experience with them will be like yours ZZT and they will provide better performance than HS6, and at a lower power factor.

 

ZZT, you mentioned

On 8/10/2022 at 10:19 AM, zzt said:

The next thing I would do is slug your barrel.  38S barrels are nominally .356" dia.  STI probably used the same blanks for 9mm and 38S, but it pays to check.  If your barrel is .356", then .355" bullets are not a good idea.  You might even try some 124gr .356" HAPs just for fun.

by any chance do you have any personal experience trying/experimenting with different bullet diameters and all else the same, and reaching any conclusion as to what provided the best accuracy?  So for example, if my barrel slugs out at .355, would bullets of .355 or .356 or even .357 diameter be best for accuracy?  Certainly I get that a bullet of smaller diameter would be detrimental tot accuracy.

[timothy]

meaning a bullet of smaller diameter than the barrel, would be detrimental to accuracy.

[zzt]

16 hours ago, timothy said:

by any chance do you have any personal experience trying/experimenting with different bullet diameters and all else the same, and reaching any conclusion as to what provided the best accuracy?  So for example, if my barrel slugs out at .355, would bullets of .355 or .356 or even .357 diameter be best for accuracy?  Certainly I get that a bullet of smaller diameter would be detrimental tot accuracy.

 

Some, but it will probably not help you.  All of my 9mm barrel slug out at .355" nominally.  One is .355" on one axis and .3555" rotated 90 degrees.  All are very accurate with .355", so I never tried anything larger.

 

All three of by 40 barrels were .400".   Rainier .355" plated where super accurate, as were Montana Gold 180 JHPs (.355").  Berry's at .356" were the next most accurate.  X-Treme at .355" where nowhere close.  I tried some Frontier plated and they were horrible.  So you don't know until you try.

 

Matt Dardas was a great bullseye shooter and an even greater bullet maker.  I had several great conversations with him about bullet sizing and accuracy.  He was a proponent of slugging you barrel several times to find out what yo were working with.  I ordered several calibers of his pure lead slugs.  His were round and soft.  He suggested not using hard cast unless you had no choice.  Since my main interest at the time was 45 bullseye accuracy, we focused on that.  He said that in a .4515" barrel, most of the time he saw .452" lead bullets as being the most accurate.  However, he often found the .453" or larger produced the best groups.  Once he found that a .450" diameter was best.

 

I ordered several small bags of his .451", .452" .453" 200gr assortments and followed his advice.  It is the same advice I'll give you.  You'll never know until you try.  Several manufactures will sell you 25 bullet sample packs.  Several offer multiple bullet diameters in the same caliber.

 

 

[HesedTech]

On 8/7/2022 at 1:00 PM, timothy said:

So here's my question, I am interested to hear any constructive feedback on whether this is likely to happen. 

Here's my answer, listen to Cha-Lee.

 

USPSA shooting is not about bulls eyes, so experiment until you find what works for you consistently. Make sure your gun runs at the pace desired. I see way too many open shooters who consistently have issues with their loads, feeding, and function of their gun. 

 

Again, Cha-Lee knows what he talks about, it's good advice.

[zzt]

3 hours ago, HesedTech said:

USPSA shooting is not about bulls eyes, so experiment until you find what works for you consistently

 

Correct, unless you want to shoot at A zone heads obscured with a no-shoot, or the 1" top of a popper sticking up behind a hard cover barrel.  Then you want bullseye accuracy.

 

Also, it is downright foolish to imply accuracy doesn't count for USPSA.  It counts everywhere, except maybe in hand grenades.  Consider this.  Your gun/load only shoots 3" groups at 15 yards.  You are reaching around a barricade to shoot at a partially occluded target.  Leaning as far as you can without a foot fault, you can see 1" of A zone.  So you aim for the perf between A and C.  What are your chances?   Not good.  You have a chance of hitting the barrier, and a much better chance of landing in the C zone.  And you are going to shoot twice.  So odds are you are 2 or 4 down depending on PF, or 10 or 20 points down if it goes the other way.  And THIS is if you aim properly and break the shot cleanly.  Crappy ammo.  With either on my Open guns there is a 100% chance of a A zone hit as long as I do my part.

 

I'd much rather know my gun and load are perfect, and it is me screwing things up.

[GigG]

9 minutes ago, zzt said:

A zone heads obscured with a no-shoot,

 

Appendix B1

Minimum A-Zone Requirements for USPSA and IPSC Targets

USPSA target: At least 25% of the lower A-zone, or the entire upper A-zone, must remain visible around hard cover or overlapping no-shoots.

[zzt]

2 hours ago, GigG said:

SPSA target: At least 25% of the lower A-zone, or the entire upper A-zone, must remain visible around hard cover or overlapping no-shoots.

 

And that is just how they are presented.  Complete upper A zone with no-shoot right on the lower A zone perf.

[HesedTech]

1 hour ago, zzt said:

 

And that is just how they are presented.  Complete upper A zone with no-shoot right on the lower A zone perf.

Seen and shot lots of head shots and the normal accuracy of USPA gun works just fine. Trigger control on difficult targets is everything. BTW, from level 3 to local matches the only time I’ve seen only the upper A zone, at the perf, available was when a swinger wasn’t activated yet, giving the shooter an option.

 

 

[zzt]

1 hour ago, HesedTech said:

BTW, from level 3 to local matches the only time I’ve seen only the upper A zone, at the perf, available was when a swinger wasn’t activated yet

 

Good for you.  CoF designers around me do that all the time.  Your def of accuracy may not be mine.  To each their own.