9 Major Barrel losing velocity? Barrel Shot?

[Jimboslice]

I'll try to get this as complete and concise as possible since I couldn't really find a whole lot while searching,  so here we go I currently have 2 CK 9mm open guns (1 Hardcore (main gun, 12-14k rnds) , 1 Thunder (Backup, 3-4k rnds.)) and I'm trying to figure out what is going on with my main gun making PF.

 

A little back story...I just got back from A3 and I barely made major (165 even) with my main gun but made it just fine (172) with my backup and the same ammo (guy on my squad was having gun troubles). I shot this same batch of ammo (loaded it all this winter ) at A1 and made major easily there (174) in march.  So I got back home last week, took my chrono out,  and shot a random mix of the ammo I had left from A3 through both of my guns, thinking that their chrono was slow or that the humidity had some effect on things (aka trying to find excuses),  and pretty much got the same results that I did from A3. So being frustrated with those results I went home and loaded some hotter rounds (7.4 & 7.6),  than what I normally load (1.165" OAL,  7.2gr Win 572, 124gr MG JHP, WSP, mixed brass), and came back with pretty negligible increases in velocity. I still have yet to try a different lot of powder or primers to see if that's the case but I plan on doing that this week.

 

Is it possible that the reason that it's doing all of this is because my barrel is shot out? I forgot to check accuracy but I plan to do that as well this week.

 

Thanks,

Jim

 

 

 

Edited August 14, 2017 by Jimboslice
more concise title

[Steve RA]

More than likely the barrel, you could get a sample pack of bullets greater in diameter than what you are currently using and see if that picks up the velocity any.

[Jimboslice]

Thanks Steve. I figured that could be the case with what searching I've done. I've also got some 147gr AA loaded ammo and some PD 124s & 115s bullets to check as well. 

[jcc7x7]

If the bbl is shot out in 12-14k's rounds that speaks very poorly of Win 572.

The MG bullets are not a variable with bbl wear.  I along with 1000's of other guys have 40-80+k of MG's down bbl's with no appreciable loss in velocity.

Check the throat of your bbl. . i.e. where the rifling starts in front of the chamber and let us know how it looks.  Is the rifling sharp there or is it eroded away.

Be honest I'm very surprised your bbl is slowing down with only 12 to 14 k through it

Edited August 14, 2017 by jcc7x7

[Aircooled6racer]

Hello: Clean your barrel and look at the throat area to see if it looks out of round. Measure the Montana Gold bullets to see if they are on size. Win 572 is a hot powder from what I have seen around here in 38SC and 9mm. Certain barrel companies are known to have good and bad quality barrels come out of there doors. You may have a bad one? Thanks, Eric

[Jimboslice]

TL;DR   The average velocity between the 2 guns there was an approx. difference of 2.3%. Is that enough to be worried about? I was in a rush and forgot to take a target out so I didn't check accuracy.

 

Full story:

When I got home yesterday I pulled both of my guns apart and compared the barrels. From what I can tell on my main gun there is maybe 1 rifling "lug" that looks a little eroded compared to the others. I also grabbed a loaded round and tried it in each barrel to see if I could feel any differences in the chamber between the two. I found that on the problem gun, the chamber was a tad longer in comparison to the top of the barrel lug (~0.020") and had more play on the sides than the other gun. After I did all of that, I cleaned both barrels up, and tightened the comp on the problem gun (noticed it had about 3° of rotational movement). I shot 3 rounds out of each gun of 147gr. AA factory ammo and some 124 PDs that I loaded to the same charge and OAL. 

Below is the table of the shots:

 

	124 PD, 7.4 grn 572, 1.165" OAL
	Backup Gun		Main Gun
	FPS	PF	FPS	PF
	1390	172	1348	167
	1402	173	1370	169
	1400	173	1373	170
sum	4192		4091
avg	1397.333		1363.667
velocity difference		33.66667
% difference		2.41%

 

	147gr. Atlanta Arms 9major
	Backup Gun		Main Gun
	FPS	PF	FPS	PF
	1207	177	1179	173
	1196	175	1171	172
	1195	175	1167	171
sum	3598		3517
avg	1199.333		1172.333
velocity difference		27
% difference		2.25%

 

Thanks,

Jim