Perplexing Accuracy Issue


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sbrader
June 23, 2012, 08:17 AM
I was at the range with my son yesterday. I had loaded up a bunch of .40 for his XDSC. I gave him two batches of 50 rounds. They were both 175 gr SWC, 1.124 OAL, crimped to .422. The only difference was that one was loaded with 5.3 gr of Unique and the other was 5.6 gr of Unique. The 5.6 gr rounds shot wonderfully. The 5.3 gr rounds were all hitting about four inches low. He would switch between the batches from mag to mag and the 5.3 gr rounds were consistently about four inches low. Granted, this wasn't from a rest, but the rounds were punching perfect little groups about four inches below the POA.

I still have some headroom in the data to take the powder charge even higher than the 5.6 rounds, so I will keep working up. I was starting at the start data point in the data I have and working up.

I asked this on another forum and have largely gotten advice to just shoot the better load. Well, I'm certainly not planning on loading the same as the ones I have had problems with, but I am hoping that someone can point me in the right direction as to why we are seeing this.

I am totally perplexed! Any suggestions from the experts (or even the not-so-experts)???

Thanks,
Scott

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Blue68f100
June 23, 2012, 09:59 AM
When shooting lead, bullet fit is a must. At the lower pressure the bullet is not sealing off against the bore and your getting some gas cutting/leakage around the bullet. This can happen with harder cast bullets and light loads if the bullet fit is not right. But normally if the bullet is fitted right this is not a issue. The higher charge is forcing the lead to seal against the bore giving you a more accurate round. Keep the charge up and you will be fine.

Josh45
June 23, 2012, 11:03 AM
Pretty much what Blue said.
When I shot 230 Gr Hornady LRN bullets out of my gun, It leaded up pretty badly and due to that, My shots were at the edge of the target at the bottom and I was aiming for bullseye just like anyone else would have.

1. Make sure the lube is a god lube, IE, No leading caused after shooting a few.
2. Bullet to Barrel fit. Seriously important with lead and can help accuracy.
3. The charge is to slow to seal off the gases in the chamber like Blue said.

Stick with the higher charge ( duh ) and you should be good to go unless you want to experiment with the lower charge., It's Ok....It's what we do as reloaders lol

bds
June 23, 2012, 11:58 AM
I still have some headroom in the data to take the powder charge even higher than the 5.6 rounds, so I will keep working up. I was starting at the start data point in the data I have and working up.
Good plan.

Benefits of conducting a full powder work up initially with a new powder/bullet combo is that you can identify the charge that starts to reliably cycle the slide and eject the spent cases, charges that produce acceptable/most accurate shot groups and other factors such as POI vs POA, recoil and how clean/dirty the powder burns for each charge, etc.

This way, you can identify the loads you want/need from the very beginning without trial and error or guess work. ;)

ArchAngelCD
June 24, 2012, 12:29 AM
Technically the lighter load isn't a problem, it's just shooting lower but giving you good groups from what you said. If you wanted to keep using that load you can adjust the sights to POI of aim 4" higher.

I would find the most accurate load and make the adjustments for POA=POI. It's perfectly normal for loads of different pressure or velocity to have a different POI. There is nothing wrong with any of those loads unless they group like a shotgun pattern.

gamestalker
June 24, 2012, 03:48 AM
Sight adjustment vs desired velocity is the only area of consideration in my opinion. If they group tight then make the adjustment as per POI and then you'll be good to go.
GS

If you decide to try other powders, you might want to try HS6 or Longshot. I have had very consistet results with either of those powders with far less POI issues to cope with. This is probably more due to the burn rate keeping pressures closely compatable I feel. Slower burning powders will have a smaller margin of pressure deviation than a faster powder such as Unique. Nothing wrong with Uniqure, it's good stuff, it just reacts with less pressure variance to small deviations in powder charge than than slower burner's.
GS

popper
June 24, 2012, 07:13 PM
Like gamestalker said, or HP-38/W231. You didn't state cast or the distance. I assume also a short barrel. Faster powder may give a better burn. There is also the problem of flip/recoil to consider. I use 5.0 of unique with that cast bullet in a 4 1/2" bl, shoots a little HIGH.

redneck2
June 24, 2012, 07:29 PM
Generally, the slower loads hit higher. This is due to the dwell time in the barrel. Allows the recoil to raise the barrel slightly more.

Where do these fall within the recommended charges? Min, max, etc.

FWIW...I've gotten away from Unique and gone to Universal Clays. Typically uses about the same charges and gives virtually the same results, but considerably cleaner.

sbrader
June 25, 2012, 02:54 PM
I'm using a 175 gr cast SWC in a three inch barrel. I suspect that the bullet is not obturating properly and we are seeing the result in the POI. I have switched from cast bullets to Precision Delta FMJ and JHP in my 9mm with excellent results. I am planning on moving to those for my son's .40 S&W, also, and try to work up new loads. I am using Unique because it is so versatile and was a great powder to start reloading with. As I have gained experience I have developed a desire to work up some loads with other powders, also, to see what works best in our handguns. Fortunately, I have a friend with a stock of about a dozen powders that I can get small quantities from for testing before I spring for the whole pound.

Thanks for the suggestions on the problem.

Scott

sbrader
June 25, 2012, 02:56 PM
"Where do these fall within the recommended charges? Min, max, etc."

The minimum I came up with after consulting a number of sources that don't necessarily agree is 5.2 grains with a maximum of 6 grains. For whatever reason, my son's XDSC is not happy with 5.3!

Scott

popper
June 25, 2012, 06:54 PM
son's XDSC is not happy with 5.3! I assume you mean it won't cycle properly. XDs have a strong recoil spring. A full load with unique probably WON"T burn completely in a 3" barrel. Go to a faster powder. If the fit isn't correct you get a pattern, not a group. Drop is fps or flip. Period. I suspect that the bullet is not obturating properly and we are seeing the result in the POI nope, that would be fit and causes BIG groups, not drop.

Innovative
June 25, 2012, 10:31 PM
I've been shooting the Glock 27 (.40 Cal.) for over 15 years, and I finally found a very impressive accuracy load. Nothing else even comes close. It's a 155 gr. Speer Gold Dot H.P. bullet with TiteGroup powder and a Federal primer. Velocity is subsonic (1,050 fps).

This load functions perfectly, recovers from recoil quickly, and provides enough punch to do the job very well.

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