.30 v .303

[bonza]

The only .30 caliber rifles I own are .303 British, & have always used Hornady .30 caliber gas checks. Looking at Pat Marlin's Checkmaker list of sizes available I see he shows both .30 & .303, what is the difference?

[Winger Ed.]

.30 cal. bullets are typically sized to .308 or .309 dia. (7.62 mm bore diameter)
The .303 is more like .312-.314. (7.7 mm bore diameter)

The .303 gas checks will fit better for the slightly larger bore diameter & boolits for it.

[M-Tecs]

Designed for .308" groove diameter barrels verse .311" groove diameter barrel would be my guess but send him an email to get 100% correct info.

[JonB_in_Glencoe]

The only .30 caliber rifles I own are .303 British, & have always used Hornady .30 caliber gas checks. Looking at Pat Marlin's Checkmaker list of sizes available I see he shows both .30 & .303, what is the difference?
"what is the difference?"
About .003"
But, that all depends on your boolit mold and the diameter boolit shank is makes on your boolit.
Typically it's close enough to use same GC.
https://castboolits.gunloads.com/showthread.php?11997-Gas-Checks-vs-Shank-Size
If you are having issues installing a Homemade GC, changing the material thickness can sometimes solve the problem.
Another thing that can be done, is to change your alloy or casting technique to alter boolit shank diameter.
That's my 2¢

[BJung]

I've started casting .311 bullets for my T99 and am interested in gas checks for my cast bullets. I used .308 gas checks with decent results but am concerned that gas will cut past the bullet with the wrong size gas check and effect accuracy. Has anyone compared shooting a .308 gas checked cast bullet vs a .312 gas check cast bullet in a .3115" or so bore and observed improved accuracy?

[AviatorTroy]

I have used the hornady .30 caliber gas checks on .303 Brit, 7.7 Japanese and both flavors of 7.62 Russian with no problems whatsoever. I have also “beagled” plenty of different.308 molds out to experiment with .303 British although I have more or less settled on the Harris 160gr spitzer designed for the 7.62x39 beagled out to throw about .314. Gas checks still snap on easily with a little pressure before going through the sizer. Hope that helps.

[Travisbishop]

I use checks on my 303's that are .314, then lubed and sized to .312. I also check the hunting rounds for my Remington 81 in 35 Remington. I've never powder coated, but want to check it out

[Bloodman14]

Using roofing flashing and Pat's Checkmaker, I have had no issues at all checking anything (4 different .30's, 2 of which are Enfields).

[Patrick L]

BJung,

No worries there. When you size the bullet and apply the gascheck, the die will swage things out to whatever diameter you are sizing the bullet.

I have used regular .30 caliber checks for years in my Type 99, and accuracy is fine.