Shooting for Groups with a Magazine

[SES50]

So I am getting ready for my Colorado elk hunt this year and have been working on putting together a 300SMK load for my 338 Lapua. I spend a good amount of time on different load combinations of H1000 with Fed and CCI primers. The COL is set that I just fit into my magazine which puts me about .030" off the lands. Not ideal but at least I can get multiple rounds in the rifle.

I went to the range this weekend and started shooting at my target over my crono and the extreem spreads were up in the mid 30fps. The yardage to the target was 436 yards and my groups were not all that impressive. So half way through I thought, "maybe the recoil is pushing the bullet further into the case which is why the spread is so wide. So I started single loading them and the first group of 5 had and ES of 15fps. The second group of five had an ES of 9 and the last group had and ES of 11. Wow, that sure changed things.

Anyone else run into this situation? Anyone else have a good solution to deal with this in a hunting situation where I would like to have more than one round in the rifle at any give time and still have good accuracy?

Thanks
SES50

[davewilson]

2 questions, do you have a brake on that thing and how much squeeze do you have on the bullets?

[Rymart]

Muzzle break/better muzzle brake - more neck tension (bushing dies) - crimp - heavier rifle...

Also using the 300 SMK's out of the 338 LM this year, with RE25 and 215M's. Haven't tried it over a chronograph, but magazine fed groups seemed good. I'm using the 0.365" bushing (not a lot of tension), a DE Brake, and about a 12.5 lb rifle. Might try a 0.364" or 0.363" bushing for next year.

I used 250 gr SGK's two years ago before I had a muzzle brake on the rifle. Shot great when single fed...big problems when magazine fed...



Good thing I only needed one shot!

[mattj]

I find this interesting --

If your rate of fire happens to vary significantly, that could explain it as well (barrel/chamber temp, etc).


If you want to prove or disprove your theory, I'd suggest measuring the seating depth of the last round in the magazine before and after it being in the mag while the other rounds are fired, then you'll know for sure whether the seating depth is in fact changing.

If it is, you may have to polish down your sizing button (or use a smaller neck bushing if you do it that way) to get more neck tension.

[loaders_loft]

get yourself a lee factory crimp die, if indeed the col is being reduced by recoil. Or, maybe its time for a stonger magazine spring to hold the rounds more tightly in place. That's my opinion, probably others have more ideas for you.

[royinidaho]

That's why I glue in the follower with no mag inlet in the stock.

I always shoot single shot.

It's kind of cool plus I've never hit anything with rapid follow-up shots.

[SES50]

Dave: DE 4 Chamber Brake, 12lb rifle. I am currently using a redding .365" neck bushing.

Rymart: That is what my 225 Accubonds look like.

MattJ: I was thinking about the chamber heating as I was driving home from the range. I will take my calipers out next time I go.

I have a .364" neck bushing. I may also look at using that on the loads for this next weekend. I would consider dumping my magazine as a last resort, as I did get a buck this weekend with a quick second shot. The head shot at 473 yards just missed him and he jumped up and gave me a perfect side shot at the same yardage.

I have also thought about making the seating depth a little deeper as well to give some leeway with the front of the mag but this may effect accuracy as well. Thanks for the ideas. If anyone else comes up with other ideas I would like to hear them.

Thanks
SES50