9mm velocity difference, 2 guns


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sublimaze41
December 19, 2007, 05:14 PM
Thanks Cabelas. Free shipping on 3,000 115gr FMJ HB for $183. Merry Christmas to ME. Got 'em and of course I had to load and test some. Since I had 8# of #7 I got for my birthday it seemed to be coming together very well.........

Below are the details, but here is my question. I loaded up several hundred 9mm rounds with 115 Winchester FMJ HB using 8.3 grains AA#7. The OAL was 1.14 and all the brass was once fired. I went to the range and chronographed the rounds from a Sig P228 and Glock 19. The rounds fired from the Glock were 61 FPS faster. Both guns are standard carry with no modification. Is there a simple reason for the differences in velocity :confused:

Sig P228

15 shot
FPS 1015
SD 15
ES 53
Hi 1040
Low 986

Glock 19

19 Shot
FPS 1076
SD 25
ES 97
Hi 1121
Low 1024

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LexDiamonds
December 19, 2007, 05:18 PM
No two guns will shoot the same. You could have expierenced the same spread even in 2 G19s. Its possible the polygonial rifling in the glock lends itself to slightly faster speeds.

strat81
December 19, 2007, 05:22 PM
The Glock's barrel is 3mm longer, according to data I found. Does the Sig have traditional or polygonal rifling? That may affect things too.

CZ57
December 19, 2007, 05:39 PM
Both replies are correct, IMO. The Glock's barrel is slightly longer and the Sig has conventional rifling, although I don't put as much stock into the claims for higher velocity that Glock would have you believe, and H&K was doing this long before Glock.

AA#7 is an exceptional 9mm powder. That's what it was made for. But, to really get the most of it's velocity potential, you'll probably have to consider a couple of things. A longer barrel, or higher charges. If velocity isn't a real concern, don't worry about it. You can still get exceptional accuracy as long as you are closer to the listed max for chargeweights. AA#7 will generally be about as low in pressure as you'll find with 9mm loads of 124 grains and higher. Accurate's max charges are fairly conservative in terms of pressure. It would be nice if there was comprehensive +P data. While #7 was formulated specifically for high velocity 9mm Nato, High velocity is the keyword. ;)

I don't use #7 with 115 gr. bullets, there are plenty of powders that will get you the same results. But when you move up to 124 grains and higher, especially 147 grains, there aren't many powders that will achieve higher velocity for pressure generated.

sublimaze41
December 19, 2007, 05:47 PM
I favor AA#7 for 2 reasons. One, I gotz 8 pounds and second, because it meters very well in my 550b. A double charge is very difficult with #7 as well. I ran a few numbers and if I switched to AA#2 I could get about 650 rounds more out of a pound.

fineredmist
December 19, 2007, 05:52 PM
The 3mm of additional barrel is not a factor here but the polygonal rifling is. The polygonal rifleing permits a tighter seal with the bullet increasing the velocity. There are several factors that effect the velocity and they can vary between guns of the same make and model.

sublimaze41
December 19, 2007, 06:02 PM
This seems to be a good example of why working up loads is important. Granted my charge is kind of middle of the road, but a load that's safe in one gun might need to be closely monitored in another.

Jim Watson
December 19, 2007, 06:17 PM
Note that the velocity spreads overlap.
Shoot a hundred more in each and see how they compare.

sublimaze41
December 19, 2007, 06:25 PM
Jim,
Can you explain that a bit more?? "velocity spreads overlap"

CZ57
December 19, 2007, 07:02 PM
It's more than polygonal rifling and bullet seal. Take a Glock 17 and a Ruger P-87. They both have 4.5" barrels, but velocity will consistently run higher in the Ruger. Hardness and quality of steel is a very much overlooked aspect. SIG steel is as good as it gets, but I think you'll find their barrels tighter than most.;)

Jim Watson
December 19, 2007, 07:28 PM
"Velocity spreads overlap" means that your fast shot with the P228 is higher than the slow shot with the G19. Means that the statistical significance of the differences in averages is pretty weak and it would take a lot more values to show the real difference.

jfh
December 19, 2007, 07:50 PM
Jim Watson's on the right track. These two guns really do look awfully similar here--run chronos on 100 rounds from each and we might start to see the significance.

If your chrono has output, run the data into a spreadsheet and look at a couple of different kinds of graphs.

Jim H.

Walkalong
December 19, 2007, 10:03 PM
Fire 8 rounds and log data. Fire 8 more, same load, same pistol. Log data. It might suprise you. Like the guys said. To tiny a sampling.

sublimaze41
December 19, 2007, 10:12 PM
Great advice, Thanks. I like the velocity of the rounds and they cycle great. The last test will be in my P7M13, although that gun will digest about anything.

I was testing the load that is described above for safety and feeding. When I noticed the velocity difference it got my attention. I guess it is safe to say this is a very safe load. Fine FPS for your basic FMJ

Steve C
December 19, 2007, 10:34 PM
I consistently get velocities from my Glock 19 that equal or exceed longer conventional rifled barrels of full size service pistols when shot with the same ammo (both hand loads and factory) under the same conditions on the same day. The comparison pistols where a Bernetta 92, Browning HP and Taurus P92.

Personally I think the polygonal barrel makes up the difference in barrel length.

The only AA7 loads I've chrono'd was an 8.0 gr start load behind a 115gr JHP Remingotn lit off with a Federal primer out of mixed cases. That gave me a 5 shot average velocity of 1,163 fps with a STD of 9.24 and extreem velocity spread of 1,155 to 1,179 fps out of my Glock 19.

CZ57
December 19, 2007, 10:53 PM
Well, the P7 will make things interesting but it also has a polygonal bore. What would make things even more interesting would be to include a 4" Springfield XD and any 4" Walther. Walther is second to none when it comes to barrel steel and it may seem odd, but those Croations are making some pretty good steel as well.

You guys (JW in particular) already have the overlap question resolved. IMO, we're talking about more than overlap here.;)

uneasy_rider
December 20, 2007, 10:35 AM
You are only talking about a 60fps difference on average between these two barrels.

I don't think this has anything to do necessarily with the type of rifling. It might, but I have seen that much variation in two of the same type of gun with the same length barrel.

Also, on your Glock, the SD is 25, which means that about 75% of your rounds will be within a 50 fps spread of your average. So really, the 60 fps difference between these two guns is nothing important or unusual.

In various 1911's, all with 5" barrels, I have seen that much spread and more.

CZ57
December 20, 2007, 06:08 PM
UR, I agree. I believe if 10, 10 shot strings were fired from both pistols, the results aren't going to vary by much. From my own experience with SIG 9mm autopistols, I have found them to have tight bores and at equivalent barrel lengths, they won't be the velocity champ. Then again, you probably won't need to worry about replacing a barrel with fewer than 20,000 rounds, and that might be conservative.

I've seen several tests conducted where velocities from a 4" XD (Walther P-99 as well) with conventional rifling, exceeded those from a 4" Glock with a polygonal bore.;)

sublimaze41
December 20, 2007, 07:24 PM
I appreciate all the great opinions! I came home from the range and was clueless about the results, within minutes of posing my question different ideas were posted. That is the great thing about THR, you get the benefit of many years of experience, and unless the situation is dangerous people rarely beat you over the head about your questions. Since visiting THR I have saved a bunch of money, improved my shooting and strengthened my safety. Many Thanks

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