Bore dia vs powder charge ???

[Rockchuck]

I have a 20 vt with a mullerworks barrel
The bore dia is .200 I noticed most 20 cal barrels have .199 bore dia. I have also noticed that most guys say 18.0gr of h4198 is a pretty stiff load. In my rifle 18 gr doesn't show pressure signs at all. In fact I have been slowly working up to 18.8 gr and the primers are still showing nice round edges. I also notice the case necks are very dirty. It seems like the load is still mild no loose primer pockets. Waiting on a new magneto speed to check velocity. Any thoughts? Might add these are with 40 gr bullets

 

[TAJ45]

Just a shotgun answer and some may be really minuscule/whacko for cause.
Case brand? Large internal volume? Primer on bottom end of brisance scale? Need more neck tension, powder too slow?

 

[AJC]

Maybe your bore is loose. Do you have a long freebore

 

[Rockchuck]

Maybe your bore is loose. Do you have a long freebore

Zero freebore,lapua brass,rem 7 1/2
Primers
I might add the rifle shoots great,rarely ever goes over 1/2" groups if it ever has. Just curious

 

[Webster]

I have a 20 vt with a mullerworks barrel
The bore dia is .200 I noticed most 20 cal barrels have .199 bore dia. I have also noticed that most guys say 18.0gr of h4198 is a pretty stiff load. In my rifle 18 gr doesn't show pressure signs at all. In fact I have been slowly working up to 18.8 gr and the primers are still showing nice round edges. I also notice the case necks are very dirty. It seems like the load is still mild no loose primer pockets. Waiting on a new magneto speed to check velocity. Any thoughts? Might add these are with 40 gr bullets

You don't need to keep increasing the load just because you think you can get away with it. Go for accuracy at a decent fps. varmints don't know the difference.

 

[Kurz]

I have a 20 vt with a mullerworks barrel
The bore dia is .200

How do you know the bore diameter is 0.200?

Is the groove diameter 0.204?

Did you call Mullerworks?

 

[Rockchuck]

Yes that's what was stamped on the barrel .200/204. Slowly push up to 19.0gr had a little heavy bolt lift. I can shoot 18.0 gr easy. Shot some groups today with 3 different loads 17.8,18.2,19.0 they shot in the 2's except the 19.0 it shot in the 4's. The bullets are 40gr bib bt. Man do they shot. When I get get my magneto speed I will check velocity. I have also had some fine groups around 17.5gr range also. All loads where h4198

 

[FrankG]

Your bore could be .2003” or .2004” or .2001” etc...Unless you know to the 4th decimal place your guessing.

That being said we only stamp our barrels to the 3rd decimal place most of the time. We run min spec tolerances which is size +.0005”.

Back to the original question....

SAAMI spec on bore size is .2000” + the tolerance.

We are tooled for both .199” and .200” bore size .20cal barrels.

Bore size doesn’t effect pressure as much as the groove size does. It still effects it but not as much as the groove.

Later, Frank
Bartlein Barrels

 

[gunsandgunsmithing]

Your bore could be .2003” or .2004” or .2001” etc...Unless you know to the 4th decimal place your guessing.

That being said we only stamp our barrels to the 3rd decimal place most of the time. We run min spec tolerances which is size +.0005”.

Back to the original question....

SAAMI spec on bore size is .2000” + the tolerance.

We are tooled for both .199” and .200” bore size .20cal barrels.

Bore size doesn’t effect pressure as much as the groove size does. It still effects it but not as much as the groove.

Later, Frank
Bartlein Barrels

Yessir, I believe that. I had a .2990 30 cal bbl made and really saw no difference in loads, speeds or pressures from it. Shot very well. And yes, of course that is diameter at the lands, not the groove diameter.

 

[L.Sherm]

18.3-18.5 in that neighborhood always shoots the best the 20VT.
I've got a couple GM 20 cal barrels that are .200 there a little slow but they seem to shoot just fine.
I do prefer a .199/ .204 3G 20 cal barrel

 

[clowdis]

So, grooves only .002 deep on .20 cal.?

 

[L.Sherm]

18.3-18.5 in that neighborhood always shoots the best the 20VT.
I've got a couple GM 20 cal barrels that are .200 there a little slow but they seem to shoot just fine.
I do prefer a .199/ .204 3G 20 cal barrel

One thing I want to clarify is the 18.3-18.5 is with a 32-34 grain bullet

 

[FrankG]

So, grooves only .002 deep on .20 cal.?

Yep according to SAAMI spec.