.236 vs .237 ???

[65BR]

6mm BR 4 groove, 24" finish, will shoot more 105-107s but want to dabble w/70-87s also.

Pro's/Con's.....What's the trend???

 

[Bob3700]

With a .236 bore you have a little more thickness in your lands. The HP group seems to favor the .236 while benchresters tend toward the .237.

Perhaps the .237 engraves their light short bullets less and at short distances, makes tighter groups.

Haven't seen any testing that confirms that. I believe it is just people's opinions and you know what they are worth.

Bob

 

[HPMike800]

I'm a High Power shooter, The only opinions I've heard on it is that the .237 bore may help reduce pressure for the big 111gr-115gr bullets. Don't know.
Mike

 

[Bob3700]

Mike,

I am a HP shooter and currently have a button-rifled, .236 bore and shoot exclusively 107 SMK for 600 yds and 115 DTACs for 1K.

All bullets are coated and reach velocities over 3000 fps with normal pressure signs.

The .237 bore will obviously make a more shallow engraving on the bullet and thus may defore it less. That may be a factor for short range accuracy. The deeper engraving of a .236 bore doesn't seem to affect the LR accuracy of the bullets.

I don't know how many rounds a BR shooter gets from his bbls, but I suspect that it may be less than a HP shooter. That is just a guess on my part though.

Bob

 

[1shot]

I shoot LR and had a .236 that caused several of the J4 jacketed bullets to not arrive. Switched to a .237 and got an increase in velocity,less resistance in the bore) and no more gray "poofs". As always, YMMV,
Lloyd

 

[HPMike800]

Lloyd:

Well that's good news, What cartridge and twist are you shooting? 6XC?
Mike

 

[Obtunded]

In general, the .237 bore is the domain of 6mm light bullet/ppc shooters where they are running extremely high pressures. Nothing stopping you from using a 237 for heavier bullets as a way of offsetting pressure, but generally the 236's are better for heavier bullets

 

[1shot]

HPMike800,
I knew I should have given more details about 5 sec. after I hit the "post" button. Anyhow, I'm shooting a 6mm Super X. It's simply a 243 with a 30 deg. shoulder and a .320 long neck, or a 6XC on steroids if you will. In fact, I use a 6XC die held .120 off the shellholder and run .243 brass into the die, walla, a 6mm SX. The bbl. that gave me the trouble was a 1-7.50" twist. When I replaced it, I slowed it down a tad to 1-7.75" twist with the .237 bore and couldn't be happier. The DTAC bullets would shoot just fine in the .236, but the thinner J4 jackets wouldn't make the trip 100% of the time. I drive the 115 bullets at 3,040 give or take, because that is where they shoot well. I hope this helps,
Lloyd

 

[HPMike800]

Loyd:
Thanks, That's what I thought when I read your post. I have a 1:7.5tw .237 bore I'm going to cut into a 6XC for 115's. Hopefully if their coated, they'll make the trip. Hopefully Berger will make a thick jacket 115 soon.
Mike

 

[65BR]

So if I want to shoot my 70 TNTs @3400 mv along with 105-108s, .237 is best??

Thanks to all.

 

[alf]

Depends on the diameter of the bullets you wanna shoot.
Most flat base, benchrest bullets have a pressure ring that measures .2435 or more. That's why close range shooters can use a .237. But the long range bullets don't have a pronounced pressure ring, which by design, tend to have a smaller diameter, sometimes under .2430, which is why a .236 may be better.
To give you a for instance......
I had a barrel that measured .2367 and an early lot of 105's that measured .2435. Twas a match made in heaven........ til I ran out of the fat bullets.
Nothing's set in stone, but, Krieger generally sells .236's to the long rangers and .237 to the shorts. Frank, at Bartleins, says it doesn't make any difference, which is confirmed by a buddy's .237 shooting 105's really well.
Clear as mud?
My opinion only, says..... I know a .236 works, a .237 may work.
Twas me, I'd do an 8 twist, .236, for up to the 107 class bullets.

Al

Al

 

[65BR]

Thanks.