6mm 105 JLK and Sierra Matchkings, bullet diameters

[Englishman 17]

Hi Gents,

Can I ask if anyone has any 6mm 105gr JLKs and 6mm 107gr Sierra Matchkings can you tell me the nominal bullet diameters. I have just put a new Bartlein barrel on my 6BRA heavy gun using Berger 105gr vlds and it looks as though it is a pretty tight barrel and my rounds are showing signs of pressure and have ended up with a Mv of only 2840 fps. The Berger 105s measure 0.243 exactly but I was told that the JLKs / Sierra bullet diameters might be less than 0.243 and if used I might get something like my previous barrels Mv of 2960 fps and reduced pressure on my brass.
Any help much appreciated.
Good shooting
Les

 

[Texas10]

My 107 MK's, recent purchase, measure .2436 with my Mitutoyo micrometer.

Have you slugged your bore?

 

[Lone Hunter]

Different lot of powder or same lot?

 

[Texas10]

More questions: Is the barrel broken in yet and up to speed?

 

[Englishman 17]

My 107 MK's, recent purchase, measure .2436 with my Mitutoyo micrometer.

Have you slugged your bore?

Not yet, I thought that it would be easier to find out bullet diameters and take it from there. Thanks for the info on the matchkings.

 

[Englishman 17]

Different lot of powder or same lot?

Same lot of powder

 

[Englishman 17]

More questions: Is the barrel broken in yet and up to speed?

The Bartlein barrel has about 400 rounds through it so I would have thought it would be up to speed. But I guess all barrels are different and yes it might speed up but not sure. Thanks

 

[Ranger188]

Did you get a .236 or .237 bore?
The Lapua Scenar 105's are supposedly a bit thinner than other 6mm bullets.
If you still have trouble, give them a try. Excellent QC and shoot great, just a tad lower B.C. than others.

 

[Monte F]

I just measured several brands I have, Lapua just under .243, Berger just over. Sierra, JLK, and Nosler right at .243 on my dial calibers. Individual lots may vary slightly I suppose.

 

[243winxb]

Copper-Jacket thickness would seem to be more importent then diameters? Thicker producing more pressure. Look up old Berger bullet blow up test using 6.5s.

Lead- Sierra makes the core of the bullet from four lead alloys: 6% antimony-4% tin, 6% antimony, 3% antimony, 1 1/2% antimony and pure lead.
Antimony makes bullets harder. Harder bullets make more pressure.

 

[Englishman 17]

Did you get a .236 or .237 bore?
The Lapua Scenar 105's are supposedly a bit thinner than other 6mm bullets.
If you still have trouble, give them a try. Excellent QC and shoot great, just a tad lower B.C. than others.

Hi Ranger,
I will ask my gunsmith about the .236/.237 as I cannot remember.
Thanks for the info on the Lapua Scenar and heard this today as well so might give them a try.
Good shooting,
Les

 

[Englishman 17]

Copper-Jacket thickness would seem to be more importent then diameters? Thicker producing more pressure. Look up old Berger bullet blow up test using 6.5s.

Lead- Sierra makes the core of the bullet from four lead alloys: 6% antimony-4% tin, 6% antimony, 3% antimony, 1 1/2% antimony and pure lead.
Antimony makes bullets harder. Harder bullets make more pressure.

Hi 243,
Interesting comment about the jacket thickness, I never gave that any thought so thanks for the reply.
Good shooting,
Les

 

[Englishman 17]

Did you get a .236 or .237 bore?
The Lapua Scenar 105's are supposedly a bit thinner than other 6mm bullets.
If you still have trouble, give them a try. Excellent QC and shoot great, just a tad lower B.C. than others.

Hi Ranger,
Just checked with my gunsmith and he confirmed it is a .237 Bartlein 1 in 7 twist. He has some Lapua Scenar 105s and he is going to measure them. There is a new 100yd tunnel range near completion a few miles from me so will definitely worth trying some out to see if the Mv can be improved upon as long as they are accurate and show no pressure signs.
Good shooting
Les.