300 Winchester Mag load mystery

[kujuak]

Any ideas to explain this?
My standard load with 180gr Nosler partitions was with H4350/remington Brass/Winchester LR Magnum primer. I was getting 2950fps and<3/4" 5 shot 100 yd groups.
I decided to try some Lapua brass. Started 2gr below my Remington brass load. When I got to 1.0 gr less than my Remington brass loads.I was getting only 2850fps with some primer flattening and cratering. Accuracy not quite as good either. Besides brass change I switched to Federal LR Magnum Match primers.

H1000 ,ReL22. H4831sc gave me lower velocities, poorer accuracy, and all showed pressure signs as I tried to match the velocities i got with H4350 with my Remington brass loads. I have about 200 once fired Remington 300WinMag brass, fired in my old Remington 700AWR rifle. New loads are for my new (to me) sako 75 rifle. Exploring reloading for my hunting rifle as I have retired,got old and no more expensive guided hunts in the forseeable future.

Thinking I should maybe just go back to my "crummy" old Remington brass and plain Mag primers.

Cheers!

 

[XTR]

Did you compare velocities between the brass on the same day? Chronographs can be pretty inconsistent between setups.

 

[Mike Casselton]

Measure your datum on your older, fired brass, vs the new Lapua.
Most new 300 Win mag brass is very short at the datum until it's fired.
That's why certain companies offer 300 Win Mag long brass.
It's not longer from base to case mouth, it's longer at the datum.

 

[kujuak]

Did you compare velocities between the brass on the same day? Chronographs can be pretty inconsistent between setups.

Using Garmin Xero C1 chrono, very consistent. I used it with some other rifles/calibres, same day and results were quite consistent with readings from other days.

 

[Murray Brook]

Certain rifles prefer certain load combos. Yours liked the original load you had with said components. First thing I would do is go back to your original primer. If this does no good then I would change powder. The 300 Win mag in my experience is one of the easier Mags to load for. Velocity wise 2950 ft/sec is very easily achieved in a 300 Win mag with 180 gr bullets with several powders. JMO

 

[Coyotefurharvester]

To me it reads like you are comparing 2 different rifles. But 5 rds of partitions under 1" from a factory 300wm is pretty darn good, why change.

 

[ebb]

The owner of Broughton barrels Tim North convinced me that Winchester magnums primers were the best for my 7 ultra mag. He said he had used them for years and they always grouped better than all the rest. Maybe go back to the Win primers and see if the groups come back. RIP Tim

 

[6MMsteve]

if using new brass u will get flat primers from fireforming, disregard this if they have already been fireformed, the case will slam back against the bolt face with new brass, in which the primer will move out, with good formed cases this may or may not happen, I'm just going by my experience, I always set my headspace a little tight on the go gauge not much but some feel, I don't use a no go because headspace is set, but sometimes I use the tape method

 

[mattri]

Lapua brass tends to be fairly thick/strong. As outside dimensions are dictated by chamber this can mean less internal space. Can you weigh old/new brass? If old brass is lighter it mean more internal volume which would explain the velocity and pressure difference, which in turn could affect accuracy.

 

[kujuak]

To me it reads like you are comparing 2 different rifles. But 5 rds of partitions under 1" from a factory 300wm is pretty darn good, why change.

Sorry, not comparing two rifles.I am developing loads for my Sako 75. I am trying Lapua brass in that rifle and noted a drop in velocity. My old Remington 300WinMag rifle was mentioned only to clarify the source of the once fired Remington brass. I am not working up loads for my old Remington rifle, I have used it for my hunting rifle for almost 20 years and have a bunch of the factory Remington plain jane CoreLokt load that it shoots really well and has worked well on a whole lotta critters.

 

[steve210]

Federal primers are generally softer in my opinion and would show pressure signs sooner. How is bolt lift?

 

[ISS]

maybe try some Federal 215s.

 

[kyotekiller25]

Lapua brass tends to run a bit thicker in my experience. Thus resulting in a little less case capacity and velocity, and higher pressure sooner.

The benefits of Lapua brass are consistency and longevity. The brass has more to do with your velocity/pressure than Primers at this point. I've never seen a primer swap be 100fps difference in any cartridge.

Just going to have to rework the load with the Lapua and be content with a little lower velocity, or just go back to using the Rem brass.

 

[MikeRu]

I had a tight neck issue with Lapua brass (300 WinMag) where a bullet would not drop into a fired case, so I turned necks a little. Maybe check that.

 

[boltfluter]

I always set up my .300 Win with the headspace set by the shoulder not the belt. You could easily loose 100 fps when fireforming new brass in this caliber. Did you measure speed with fully formed brass?
Paul

 

[L.Sherm]

New brass could be easily .010 short at the shoulder ( datum) as Paul mentioned thats were I would look. Measure a new piece of brass and 3 times fired case.

 

[kevinbritvec]

Changing brass and primers virtually guarantees different outcomes. .308/7.62x51mm, but the same principle applies.

 

[kujuak]

Federal primers are generally softer in my opinion and would show pressure signs sooner. How is bolt lift?

Bolt lift normal.

 

[steve210]

If bolt lift is normal,i wouldn't be concerned

 

[nastynatesfish]

In my 300 win mag I use 180gr accubonds for hunting loads.
I use Remington brass so I do t worry about losing my petersons brass
I trying h4831sc for a few but noticed low velocity.
I went with n560 and it pepped right up.
I get 3160fps from my 26” sendero and a 74.4gr charge.