Tight Bore vs Groove Variation over normal specs

[Louis Corkern]

Good Day Everyone,

First let me apologize for a "VS" thread

As I not really wanting to debate which is better but rather am wanting to discuss ballistic data for the sake of knowledge.

Recently I had a work specific .308 built that sorta deviated from the norm of things in regards to the barrel specs. As most know there has been alot of talk and such on the benefits of tight bore barrels for the short barrel rifles to keep the MV up a little. I did not go with a tight bore barrel on this 18" barrel build. I went with a normal bore dimension but went with 3 groove configuration and honestly I only went with that due to it was immediately available as I did not research the pros/cons of such. (Hats off to Lawton for having my barreled action to me in 4 days).

Here are details of what was experienced ballistic wise:
100 yard zero
600 yard required exactly 4 mils. We even dialed the knobs to confirm that as I am not good enough with mil scope to say by looking at reticle if it was 4mils, 4.2mils.
Ammo was M118LR right from back of humvee.
We did not and I have not chronoed to check MV correctly.

So my question is what are some of you guys getting elevation wise with that ammo from the tight bore barrels?

Thanks

 

[BOLTRIPPER]

Re: Tight Bore vs Groove Variation over normal specs

tight bore 3 grove....how tight ?

i got a 6 groove tight bore @ .299......

so what is the basis for normal here....???????


and BTW....please park that Humvee next to my bunker for about 5 minutes please

 

[Louis Corkern]

Re: Tight Bore vs Groove Variation over normal specs

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BOLTRIPPER</div><div class="ubbcode-body">tight bore 3 grove....how tight ?

i got a 6 groove tight bore @ .299......

so what is the basis for normal here....???????


and BTW....please park that Humvee next to my bunker for about 5 minutes please</div></div>

Not tight bore 3 groove..normal bore dimensions lol

As for the "normal"...Kinda what I trying to gather

Sorry but Humvee is down for maintenance

 

[BLAWTON]

Re: Tight Bore vs Groove Variation over normal specs

The 3 groove is not a tight bore. The difference lies in the groove to land ratio which can be much higher in a 3 groove design. The bullet has less bearing surface contact in a barrel which will allow for higher MV's along with lower chamber pressure and allowing for more charge behind it. I dont find it uncommon to see as much as 150fps higher mv over a standard or tight bore barrel.

 

[Supersubes]

Re: Tight Bore vs Groove Variation over normal specs

I spoke with Dan Lilja a bit about his three groove barrels. His have a land/groove ratio that is the same as his standard barrels. I own two of his three groove, and lots of experience with a third. They are awesome but wouldn't describe them as fast. Not trying to refute your info Guru, just the info i have.

Later, what were the conditions that you were firing in? FFS says that the bullet would need to be going nearly 2800fps to get to 600 in 4 mils. Thats using my home range condiitons of 28.24/65deg and the advertised BC.

I don't shoot M118 or the 175 smk's but my 22" Brux gets to 600 with 3.9 mils using 155 lapua's in the above conditions.

 

[Louis Corkern]

Re: Tight Bore vs Groove Variation over normal specs

SS,

I was in Anniston Alabama. I did not bother monitoring any environmental conditions other than wind. We reverse calculated the numbers from the issued ATrag equiped PDA while on the range and it come to be 2740fps but I did not log what environmental conditions they had preprogrammed for their range.

Thanks

Some other members were there and dialed the same dope when they fired it

 

[rijndael]

Re: Tight Bore vs Groove Variation over normal specs

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Later</div><div class="ubbcode-body">I did not bother monitoring any environmental conditions other than wind.</div></div>

Occasionally, I go back and get the data from here:
http://www.wunderground.com/history/

 

[BLAWTON]

Re: Tight Bore vs Groove Variation over normal specs

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Supersubes</div><div class="ubbcode-body">I spoke with Dan Lilja a bit about his three groove barrels. His have a land/groove ratio that is the same as his standard barrels. I own two of his three groove, and lots of experience with a third. They are awesome but wouldn't describe them as fast. Not trying to refute your info Guru, just the info i have.

Later, what were the conditions that you were firing in? FFS says that the bullet would need to be going nearly 2800fps to get to 600 in 4 mils. Thats using my home range condiitons of 28.24/65deg and the advertised BC.

I don't shoot M118 or the 175 smk's but my 22" Brux gets to 600 with 3.9 mils using 155 lapua's in the above conditions. </div></div>

Yes the groove to land ratio is much different over the standard barrels. You dont gain anything if your keeping the same ratio as a normal 6 or 5 groove.