I'm having a little trouble with grouping. Here are the components:

AXMC rifle 27" non-suppressed

Berger 300gr hybrids
Lapua Brass
H1000
Federal 215M primers
Seating the bullet as far out as the magazine will let me but it puts me at .120'' off the lands (from the ogive)

SD is 5.6
ES is 13 (over 10 shots)

Grouping at 300yds is about 3.5-4"



My question is, most factory manufactures have a listed COAL of around 3.6" (Black hills, Prime, Seilor and Bellot, Ruag, etc) which is still much shorter than what I am loading.  If my math is right, loading at 3.6" would mean a .180-.200 jump which sounds absurd!

What do you think my next seating depths for trial should be or is the something else I'm not thinking of? I wish I had a range in my back yard

Thats not too bad.  Not great by any stretch, but not too bad.

Try seating them deeper, you might find a sweet spot.

And play with the amount of powder and maybe try Retumbo or some other slow powder.

I have an AI PSR and am using 300 Hybrids on top of Retumbo, Fed primers and Lapua brass.  My PSR came with a Bartlien barrel (barrels) and whatever chamber reamer Dave Tooley used.

I think I'll just start seating deeper with the same powder charge, sure hope it tightens vs opens up more

I'd go run those things .020 off the lands and work your way in. Speaking in high level terms, your best accuracy is usually from .020 to .001 off the lands.

You'll have to single load them, but that's no big deal.

AMMUNITION

I agree.  0.020" off the lands is where I would have started.

TECHNIQUE & MIND SET

Call your shots, every shot.  Think about the shot and call it.  Write it down before scoping the target.

How does your rifle shoot with, say, Black Hills, Lapua, or ABM (now Berger) ammo?  BH uses Sierra MKs, Lapua uses Scenars, ABM/Berger uses Berger. Also, has your rifle shot anything better than what you just tested?

You didn't give any indication of test results for other than that single load. Was this load the best of several tested, or the only one tested?

I tested IMR7977 and N570 with 250gr and 300gr Berger Hybrid OTM Tacticals. My rifle clearly didn't like IMR7977 (>1.0 moa) as much as it liked N570 (<1.0 moa). Your loading technique seems fine, so maybe a different powder is in order.

I've been shooting mine 0.010-0.015 off the lands. You might try some at that length, even though you don't want to single load. That may tell you seating depth is the issue for your rifle with these bullets.

I will probably load a few right off the lands while I'm at it

I use H4831SC powder with very good results.
What powder you using?

What scope are you using?

You are at 1 MOA already.  Going below that takes attention  to details.

I had to go look AXMC up -

"The Accuracy International AXMC rifle is the flagship multi-caliber rifle in the AI line."

H1000

K624i in a Spuhr one piece mount

It’s possible your rifle doesn’t like those bullets. I have a savage 110 338 FCP I reload for. I shoot 285 ELD-M with 89.8 of H1000. Getting 2780 fps.  Hit 10/10 @1000 yards last summer. Try the Hornady 285 bullets.
BTW, sweet rifle you have.

I actually saw the owner of snipers hide recommend that bullet over the 300 hybrid (after the fact I bought the hybrids).  I think he argued that with slightly higher velocity it matches the BC of the 300 going a little slower.

What is your COAL on your rounds and how far off the lands are you?

OP, don't load for the 338lm, but do for 300rum(makes 338edge if punched out) any way..be careful pushing bullets in deeper in the case or out closer to the lands with an existing charge..both directions can get you into serious over pressure conditions....If you are going to vary seating depth, back off on the charge by at least 3 grains and work toward the edge in small steps(.020") at a time until you hit the lands/max depth or you need to drop charge weight more to get there..once there then work charge weights back up...
As for powders..

Retumbo
RL-33
BMG-50
H1000
US 869
VV570
There are others, but normally these are the most used ones...Retumbo or H1000 are most used, especially in hot areas... RL-33 if your rifle likes it will generally give you the most fps all things equal(hard to find bullets that really like it).... H1000 and 50 BMG normally the lowest fps but very temp insensitive and easy....570 is supposed to be close to RL-33 but everything I see says it is a very dirty powder and leaves the chamber/bore a mess...
As for your current load..how solid is your rest and are all the screws on your rifle staying tight? I notice running hot loads many rifles will have action screws, rail screws and such always loosening up enough to cause accuracy issues..Also how clean is the bore/chamber...excessive carbon/copper buildup will cause groups to open up...Are you shooting off bags, a bipod or what? does the reticle stay on target  and can you watch the bullet hit? lots of things can affect groupings, especially on the bigger cartridges..very hard to consistently shoot small groups accurately...

I went ahead and dumped all my loads I had made because I was concerned about pressure as well once I saw how far lower the bullets sat and the powder sounded like it had very little room to shake around.

I'm using a spuhr mount that is properly torqued down to the max settings.  I will probably loosen up the barrel lock screw make sure barrel is tight and retighten the lock screw to spec.  I'm shooting off Atlas's largest bipod they make for oversized rifles and a large wishbone bag for the rear.  I do my testing in my own warehouse with flat floors and no wind.  We recycle our cardboard so we have a ton of bails stacked up against a wall as a back drop.

As a shooter, I can shoot 1/4" groups with my PRS rifle in my warehouse setting.

The factory 250gr ammo I shot made by Sellier and Bellot shot 1/4-1/2 MOA at 100yds but it seemed to take a little bit of effort to eject spent cases.

Then you and your rifle are capable of better results. It may take  different powder and/or a different bullet.

Awesome...Nice, best I can suggest before you chuck this load and try different would be to go over your loads with a fine tooth comb, including your measurements, your powder measures, and concentricity...My personal guess is as soon as you close up on the lands you will get the accuracy you are looking for, but I would still verify the above things so you can maintain the accuracy once you find it...

As far as mag length loads, I am going thru the same thing..So I have a heavy BC bullet loaded to the lands for single feed long range stuff that the scope/rifle is dialed in for and am working on a short range bullet/load that I can mag feed out of the 3.850" CIP mags...kind of a best of both worlds..the tricky part is getting the shorter bullet combo to shoot close to the same point of aim...or at least close enough I can use the kilo 2400 ballistic profile to allow for the offsets...

My ACMC shot those bullets best 20 thou off the lands.

For me the Lapua Scenars 300gr shot almost as good but could be loaded at mag length.

H1000 for both with Lapua brass.

Attached File


Well I narrowed it down to 89gr of H1000 for the charge

Experimented with 3 3shot groups at 100, each group seated .065 .075 & .085 off the lands

Load 1 had an ES of 3 but .75" group. Load 2 has an ES of 6 and .56" group.  Load 3 had an ES of 9 and a .5" group
Velocity widens, but group tightens

I'm pretty happy with it, will probably go with group 2 for my load.

I’m right around there as well (88ish gr). Looks like you found a few shooters though. Some folks like to tweak and tweak. I like to just find one that’s “good enough” and shoot the shit out of it.

Yeah me too.  If it has an ES below 20 and a group of 1/2" then I call it quits on further load development.

Unfortunately I had a learning curve on this one since I couldn't reach the lands.

You should probably focus more on SD than you do ES, but otherwise those groups look solid. I'd still be interested to see what it does .020 off the lands.

Wish I could seat .020 off but magazine only allows .065 off.  I wants muh maguhzeens!

These Bergers can handle a nasty jump and still shoot very well. They look damn near like an iceberg when you load them to mag length too.

Attached File

How much jump and what kind of groups were you seeing?

When I called berger they suggest I not jump them anymore than .060

@Regency

I went with 3.685” COAL to leave some room for meplat variances. I don’t recall my jump distance but I do know it’s impossible to reach the lands and keep them short enough to feed from the mag.

.020 from the lands. Not home now to check my coal. If you try the 285, you won't be disappointed. But as always, work up to insure the load works for your rifle.