• This Forum is for adults 18 years of age or over. By continuing to use this Forum you are confirming that you are 18 or older. No content shall be viewed by any person under 18 in California.

Bore size question

i should probably know this but I don't.

I was asking questions about ordering a 6mm barrel this morning when the retailer mentioned in his email that the bore =.236.

My question is simply - what are the practical implications of using a tighter bore barrel? What difference will it make to me as the reloaded/shooter to chose a barrel with a .236 bore over one with a .237 bore?

Thank you in advance for your input.

Gerald
 
The .237 bore size is more popular. However, the .236 bore will produce more velocity due to the decrease in surface area.
 
The .237 bore size is more popular. However, the .236 bore will produce more velocity due to the decrease in surface area.
This is not the case in the Dashers we tested. The .236 picked up the pressure quicker. It was about 50 average slower. You could load a grain more powder in the .237. This was multiple barrels. Matt
 
This is not the case in the Dashers we tested. The .236 picked up the pressure quicker. It was about 50 average slower. You could load a grain more powder in the .237. This was multiple barrels. Matt
I saw the same in the 6's, but the opposite in the 30's Fastest RUM I ever had was 5 grains under book max but it was a small diameter barrel.
 
I saw the same in the 6's, but the opposite in the 30's

This is pretty much what I discovered a few years ago when testing the .236 vs .237 in the 6mm. The tighter bore showed definite pressure signs before the larger one. This followed through a much larger sample set during the course of testing the 6mm Creedmoor. Yes, I'm aware that it is difficult to test between two barrels because of the vagaries of production but these were all Bartleins and were extremely similar in performance.

But, the .30 caliber barrels were all chambered on the .299" bore for nearly every barrel without the rise in pressure. The only place a correction was made was with the AR platform which used the .300" bore.

One of the points to consider for discussion might be the length of the bearing surface for the bullets in question. Often times, Palma shooters used to subscribe to the idea of using a tighter bore because of the shorter bearing surface of certain bullets. Thoughts?

Regards.
 
The .237 bore size is more popular. However, the .236 bore will produce more velocity due to the decrease in surface area.
The .237 bore is less surface area with a .2430 groove for both because the land height is shorter. The .237 has shallower engraving in the bullet thus lower engraving pressures normally. This normally produces added velocity.

Tim North
Broughton 5C® Rifle Barrels
 
i should probably know this but I don't.

I was asking questions about ordering a 6mm barrel this morning when the retailer mentioned in his email that the bore =.236.

My question is simply - what are the practical implications of using a tighter bore barrel? What difference will it make to me as the reloaded/shooter to chose a barrel with a .236 bore over one with a .237 bore?

Thank you in advance for your input.

Gerald
I have used both and can see no difference in accuracy, all that counts.
 
  • Like
Reactions: swd
A tighter bore marginally increases pressure. Increased pressure equals higher velocity. Or at least that's what I've read. Where did I go wrong?
 
"The .237 bore size is more popular. However, the .236 bore will produce more velocity due to the decrease in surface area."

Pure Scripture!
 
A tighter bore marginally increases pressure. Increased pressure equals higher velocity. Or at least that's what I've read. Where did I go wrong?
In our 6 Dasher barrels the .236 could only shoot upper 2900 and took as much as 2 grains less Varget. The .237 could reach 3025 to 3050. This was with 4 different barrels in both twists. I believe when putting the bulletinto the lamds the pressure gets to the case before you get the velocity. Maybe because of having to get it started or engraving it.

If pressure alone gave more velocity you could use a fast powder and get pressure. Most times a slower powder or more powder gives more velocity. Matt
 
@Matt -
Like Tommy, I see more speed from .236's (especially from Brux barrels).
My slowest barrels have been 237 Bartlien's and fastest .236 Brux.
Funny how things can very so much from person to person.....
Donovan
 
Last edited:
@Matt -
Like Tommy, I see more speed from .236's (especially from Brux barrels).
My slowest barrels have been 237 Bartlien's and fastest .236 Brux.
Funny how things can very so much from person to person.....
Donovan
These were comparing all Kreigers. I get more speed out of my Broughton 5c barrels. But that is comparing a different set of lands and 4 verses 5C. The .236 barrels could only shoot 32 to 32.5 tops, of Varget and the .237 could shoot 33.5 to 33.7. The velocity difference was almost 100 fps average.

All were done with the same reader .155 freebore. Matt
 

Upgrades & Donations

This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.


Click Upgrade Membership Button ABOVE to get Gold or Silver Status.

You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.


To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.

Forum statistics

Threads
166,261
Messages
2,215,330
Members
79,506
Latest member
Hunt99elk
Back
Top