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I have been seeing some breech face pitting recently, and I'm trying to figure out if its being caused by using CCI small rifle primers or old brass?


Im running an STI Open gun, 9 major using primary HS-6 and Autocomp. It's a KKM 5.4" barrel with 3 holes and Akai Gill comp.



I WAS pushing 124g bullets way past needed power factor, 1430~1450 FPS, thinking that the extra gas would make the gun shoot flatter, recently I did some testing with lower velocities, 1330~1370 velocity and found that the dot seems to be slightly more stable.



Im wondering if the pitting may also have been caused by the extra pressure from the hotter loads?



With small rifle primers I do not see any over pressure signs, and the primers do NOT look like they are much flatter than average. I have heard that CCI small rifle primers are getting harder? And have been toying with the idea of going BACK to small pistol primers or even SP magnum primers to help contain the breech face pitting.



My opinion is that either 1-the primers are not flattening enough to seal the cup, or 2-my brass is worn past it’s usable lifespan.



Anyone have any thoughts or experience with this? Advice?



My current game plan is first to cycle out of any brass that has been used more than 5+ times, if this does not slow down the pitting I will try using pistol primers for a few months in conjunction with the “better” brass.


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Here is a picture of the pitting after only 5000 rounds:

88458701-5AEE-46E1-842D-75187A31B71D_zps

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Ditto, srp's just hide pressure signs and have more of a tendency to flame cut the breech. I see no up-side to using srp's in open major.

imho

jj

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Hope this helps I have a tanfoglio gold custom EG 2007 9mm. With a v12 barrel. load data at 124 RN FMJ with 8.0-8.1gr VV3N37 using winchester small riffle primer. FPS 1360 average in the range of 165 PF.

I have WAC and power pistol powder That most of the 2011 open Gun use but I haven't got time to experiment with it due to time close for a big match for GBC.

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Ditto, srp's just hide pressure signs and have more of a tendency to flame cut the breech. I see no up-side to using srp's in open major.

imho

jj

This is the first reason to Not use SRP beyond cup hardness in regards to ignition that I have heard.

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Why does a SRP flame cut?

My hypothesis is that the rifle primers don't seal the primer pocket as well, allowing gas to escape.

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Why does a SRP flame cut?

My hypothesis is that the rifle primers don't seal the primer pocket as well, allowing gas to escape.

Why do they not seal as well?

Is it because they don't swell/ expand during the event of ignition?

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That's the thought I'm operating on. My only evidence is empirical, but it's good enough for me, I'm happy using SPP and my breech faces are perfect :)

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Hope this helps I have a tanfoglio gold custom EG 2007 9mm. With a v12 barrel. load data at 124 RN FMJ with 8.0-8.1gr VV3N37 using winchester small riffle primer. FPS 1360 average in the range of 165 PF.

I have WAC and power pistol powder That most of the 2011 open Gun use but I haven't got time to experiment with it due to time close for a big match for GBC.

IMO, loading to 165 is like playing Russian roulette. If for whatever reason it dips even slightly (match chrono, powder drop, temperature, altitude, phase of the moon) you'll end up shooting minor with major ammo. I load to 170-172 to account for any variables.

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I think the primer debate depends a lot on the gun, the loads, etc. I was using SPP's and they were getting kind of flat and flowing a tiny bit up around 174+ PF so I was advised to go SRP's and all of the went away. Primers are just losing some of the roundness on the corners and the breech face is just fine.

As for the PF issue, most of these guns don't flatten out until a certain degree over 170 PF so there is really no reason to even shoot for lower than low to mid 170's.

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I certainly understand having a cushion above the PF floor for match purposes. I aimed for 172 for limited.

As I am new to open I hear you saying that a 175 pf target is more about pistol performance than margin of error?

Wouldn't this target be based mostly on a pistols design parameters?

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Correct. 172 (you) 175(me) falls between "low to mid 170's.

My message was that some load to 169 and call it good but wonder why they struggle with the dot moving when, if they turned it up, would probably see an increase in comp efficiency. Some just get so used to PF cushion being the main focus in other divisions that that may carry over into open.

Edited by Sarge

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Correct. 172 (you) 175(me) falls between "low to mid 170's.

My message was that some load to 169 and call it good but wonder why they struggle with the dot moving when, if they turned it up, would probably see an increase in comp efficiency. Some just get so used to PF cushion being the main focus in other divisions that that may carry over into open.

Makes sense, thanks

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I'm planning on being in between the minor and major PF ...... enough powder to get the Czechmate compensator to help but not a full major load, if that's possible? My Czechmate is not something that I want to stress (old man on fixed income) and I'd rather give up the "Charlie" point shooting minor but sure would like to have the compensator functional. I plan on starting with the 124 gr. Berry at 6.6 gr. HS-6 and work my way up. I welcome any suggestions or comments, positive or negative :-)

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If you are not going to shoot major try the 115's. 8 grains of hs6 will not make major and give you enough gas for the comp to work.

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If you are not going to shoot major try the 115's. 8 grains of hs6 will not make major and give you enough gas for the comp to work.

If you're shooting minor I suggest 95/100gr bullets and 9gr of HS6, it should be around 155pf, super soft and flat.

If you're going to shoot 124s, you'll make major with ~7.7gr, it'll shoot flatter ~8 and anything less won't work the Como very well.

Don't stress out about shooting major in the CM, it's built like a tank :). With no holes in the barrel, 9 major is no problem.

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If you are not going to shoot major try the 115's. 8 grains of hs6 will not make major and give you enough gas for the comp to work.

If you're shooting minor I suggest 95/100gr bullets and 9gr of HS6, it should be around 155pf, super soft and flat.

If you're going to shoot 124s, you'll make major with ~7.7gr, it'll shoot flatter ~8 and anything less won't work the Como very well.

Don't stress out about shooting major in the CM, it's built like a tank :). With no holes in the barrel, 9 major is no problem.

100 and 95 grain bullets are not legal for uspsa. He did not mention that he was shooting uspsa but he did reference charlies. So I assumed he is shooting uspsa.

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Tyshoots and Kneelingatlas......sincerely appreciate the help, don't have shooters with 9mm open experience in my local. I'll get started today, pretty excited !

I am remiss in not referencing USPSA, which is my current discipline.

Edited by dkiesey

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If you are not going to shoot major try the 115's. 8 grains of hs6 will not make major and give you enough gas for the comp to work.

If you're shooting minor I suggest 95/100gr bullets and 9gr of HS6, it should be around 155pf, super soft and flat.

If you're going to shoot 124s, you'll make major with ~7.7gr, it'll shoot flatter ~8 and anything less won't work the Como very well.

Don't stress out about shooting major in the CM, it's built like a tank :). With no holes in the barrel, 9 major is no problem.

100 and 95 grain bullets are not legal for uspsa. He did not mention that he was shooting uspsa but he did reference charlies. So I assumed he is shooting uspsa.

Take another look at Appendix D1.3, the minimum bullet weight for major is 112; there is no minimum bullet weight for minor.

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Here is a picture of the pitting after only 5000 rounds:

88458701-5AEE-46E1-842D-75187A31B71D_zps

I’m contemplating refinishing this slide (gun) with NP3+ or Hard Chrome to either slow down or stop the pitting, does anyone have enough knowledge and information on either finish to recommend one versus the other?

I believe that Hard Chrome is harder but more brittle and may continue to chip away if not adhered properly to the pitted face; the guys at ROBAR have said that by polishing the surface prior to an NP3+ finish they will guarantee the surface for life from continuing to erode? Not sure if that’s a sales pitch or reality…LOL.

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If you are not going to shoot major try the 115's. 8 grains of hs6 will not make major and give you enough gas for the comp to work.

Used your recommended load and it works great, thanks.....saved me a lot of time!

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