Range Report 6mmAR vs 6.5 Grendel

[kgreylgrey]

I'm trying to compare the 6mmAR to the 6.5 Grendel and have some questions regarding max pressure. The 6mmAR is a 6.5 Grendel necked down to 6mm. Both use the same original 6.5 Grendel/Lapua brass. However, QL lists the max pressure of the 6mmAR as 58740 psi and the max pressure of the Grendel as 52214 psi.

Does anyone know of any other published pressure limits for the two cartridges or know why the 6mmAR can handle more pressure?

Is there a general or ballpark pressure limit for cartridges that are fired from an AR15 platform or does it simply depend on the actual strength of the upper receiver (bolt, carrier, billet)? I'm assuming that both of these cartridges could be run much harder in a bolt gun - could be wrong about that.

In a bolt gun, a stiff bolt lift is considered a reliable sign of high pressure. What is a reliable sign of high pressure in a gas gun?

Thanks.

 

[fx77]

Re: 6mmAR vs 6.5 Grendel

Rob Whitley is a Good Source for All your 6mmAR questions

http://www.6mmar.com/

 

[Jedi]

Re: 6mmAR vs 6.5 Grendel

Wolf need to start selling grendel Brass, along with it loaded ammo

 

[steve123]

Re: 6mmAR vs 6.5 Grendel

I use the ejector smear and primer flow as a sign for excessive pressure.There are a # of factors that can be the cause of over pressure and can be unique from gun to gun in the same chambering/load.

Another way to tell is:

If you notice that the primers go in way easier on the next loading then you were over pressure and need to back off the powder charge.

To kill two birds with one stone do a ladder test.Google it.In the end you will have a load that works for a wide range of temperatures and will always be at a sound pressure.Also your ES and SD will be acceptable.

Robert also lists his favorite loads.If you were to try some of them out I'd be willing to bet that one or more are going to work great.

To save time and barrel wear I pick a couple high BC bullets and powders well suited for them,Then do the ladder test for each with the chrono.Pick the best then try again to confirm.Then adjust seating depth and you are done in less than a hundred rounds.

If you want more speed then get one of the turbo case versions Robert offers.The fireforming is a no brainer.Just follow his instructions.

Sorry I've got no explanation as to why QL is so different.

Oh and if you are planning on using it in Scottmilks match in Phoenix and you win then I get to take home the Snipers coin for giving you such good advice.Haha

Steve

 

[trilogymac]

Re: 6mmAR vs 6.5 Grendel

What Steve said worked for me.
I worked up to the charge in Robert's listed 105gr pet load using RL-15. I told him my bullet would be a 105 Amax. Tried 27, 28 and 29. ALL groups were under an inch, with the 29gr. consistently under 5/8". Done.
Mine is a Std 6mmAR and I love it.

Hope this helps,

Trilogymac

 

[kgreylgrey]

Re: 6mmAR vs 6.5 Grendel

Steve123 / Trilogymac

Thanks for the input. I have a Grendel, but was lured to the 6mmAR because of the additional speed potential and the ability to use my existing brass. When I compare published 6mmAR loads against published Grendel loads, the 6mmAR has slight advantage in windage and a little larger advantage in elevation. The only way I could justify the new upper was if I could get much better speed out of the 6mmAR. Thus the questions on max pressure and pressure signs. The Grendels are notorious for shearing bolt lugs when the you push the published safe pressure loads.

I sure wish there were more published load data available for both cartridges that included a max load pressure value. The only pressure data I've been able to find was this
http://www.myrnaloupalmistry.com/rifle/Hodgdon_%20grendel.htm

The max pressures listed by Hodgdon are around 49000-50000 psi, but the velocities are less than the Alexander Arms published max loads and velocities. Unfortunately, AA does not list a pressure value, but the loads are reported to be safe.

I guess I'll do a ladder test until I get ejector smear/wipe and then use the low/high Hodgdon data to interpolate how much pressure it takes to produce the smear.

Again, thanks for your input.

 

[steve123]

Re: 6mmAR vs 6.5 Grendel

I believe that my friend was getting 2550-2600fps with factory loaded AA 6.5G with 123's out of a 24inch barrel.This is going off of memory.I thought,"read somewhere",this load was supposed to go around 2650fps?Maybe it is in other guns. These factory loads were not making ejector marks on the brass.

Steve

 

[ranger1183]

Re: 6mmAR vs 6.5 Grendel

I don't understand the pressure differences given by QL either.

Look at the .30-06 parent cartridge

.25-06 = 65267 psi

6.5-06 = 63091 psi

.270 = 62366 psi

.30-06 = 58740 psi

.338-06 = 65000 psi