Acceptable Chamber Variances

[mobenzowner]

In a month I have gone from 0 to 2 6mm creedmoor's. I am a reloader and loaded 105 Berger vld-h bullets in my first gun. It is a Browning HCS. The one that came in just this Thursday is a Browning composite stalker.

When measuring to the lands the X-Bolt HCS has a CLTO of 2.269"
The X-bolt CS measures 2.231"

.038 seems like a pretty wide variance to me. These measurements were performed the the same exact 10 bullets and results duplicated twice. Both guns barrels and chambers were cleaned before taking the measurements. I don't have any factory ammo to verify the will fit without jamming the lands on the shorter composite stalker x-bolt. I have shot the HCS and it shoots 1 hole 100 yds with the 105 vld-h's. Should I be concerned about the Composite stalker??

 

[BallisticsGuy]

Concerned about what exactly? You've got a potential issue but not a definite one. First thing I'd do is see where each one likes ammo set up as far as jump / CBTO. If you can get 1 load spec to work well in both rifles and you either plan to full length size every time or the chambers are otherwise similar enough to allow sharing of brass, then you're all good.

I have a few sets of rifles that share brass. My strategy for that is to have the chambers cut with the same reamer by the same smithy in blanks of the type & manufacturer and then to set the guns up for zero headspace. That allows me portability of ammo between guns. Interestingly, doing it that way I only really have to bother developing a load on one gun and then just verifying it shoots acceptably in the other. I also get to neck size only without issues.

 

[ShtrRdy]

What you're describing doesn't sound like a "problem" but rather a dimension which might affect accuracy and/or muzzle velocity.

I would be more concerned with the case base to shoulder datum dimension on the fired cases out of the two rifles. (head space)

 

[mobenzowner]

What I would be concerned about is potentially having a short cut chamber in the composite stalker. I keep brass for the 2 rifles separate, so no issue there. I have done zero load development on the CS, but believe the dimensions are different enough I will need to work up rifle specific loads, which is not an issue for me. Final concern would be if I ever decide to shoot factory ammo in what seems to be a pretty short chamber.

 

[mobenzowner]

Well I have some rounds loaded up a lot shorter than what the HCS likes. I decreased the loads by .2 grains since the bullets will be seated shorter and loaded 40.5, 40.7 40.9 grains of h4350 at .015" off the lands. That should get me in neighborhood of 2950 fps.

 

[mobenzowner]

Well this gun actually prefers the same loads(with shorter cbto) as the HCS with the longer throat. I would have expected it to prefer a slightly lower charge with bullet sitting deeper in the case.