7mm rem mag and retumbo

[Fire Hawk]

So I finally took my 26" shillen barrel 7mm Rem Mag to the range to test my handloads with 160 Accubonds and Retumbo. I am pleased to say that I am finally seeing the velocities I expect of a long barreled 7mm. 69 grains was good velocity t just over 3000 fps, but accuracy was not there. I then went to the 69.5 charge and hit about 3070 fps. And saw better accuracy. When I stepped it up to 70 grains, accuracy improved, but velocity did not change at all. I am new to the chronograph game, but I am led to believe that most likely I hit my max pressures and need to back off. Is that true?

If so, I am sad as I would like to see the better accuracy of the 70 grain charge, but want to be safe. Slight cratering on the primer, but good bolt lift.

Very high pressure signs using IMR7828 and this bullet at below max charges and only low 2900 fps ranges, so I have had to rule out that powder. Just hoping to get the most out of my rifle.

What would you do?

 

[gerry]

I would try the 70 gr charge again, there is a good chance t will be just fine. Just need to try it a bit more to be sure. With charges that big it isn`t unusual to not see an increase in speed with only going up .5 of a grain.

 

[DrMike]

Gerry has given you sound advice. I might add that if the charge proves safe and reasonably accurate, you may want to adjust seating depth to see if you can improve accuracy.

 

[remingtonman_25_06]

I shoot same combo exactly but I only get 2900fps accurately at 70g retumbo. I can go to 73g and get 3000 bit accuracy isn't there. 26" model 70...

 

[Guest]

Firehawk,
Scotty has been working with RL-25 in his 7 Rem Mag. Check out his post he is getting 3069 with a 160 AB and no pressure signs. His 200 yd groups look pretty good too.

I had good luck with RL-22 Powder when I had a 7 mag at one time, but then maybe you don't have access to these powders where you are located.

Retumbo powder is an excellent powder but my experience using it in my 300 RUM revealed it peaked faster than most I have tried.

Good luck developing that load recipe, keep us posted on your results.

Don

 

[Fire Hawk]

Thank you for your help. I will keep playing with the Retumbo and see how it goes. I was really happy to see the velocities get into the realm of where they should be.

 

[338 Ultra]

Like Dr Mike said much good advice here and working your oal to find the right jump. I don't have a single AB load in a variety of calibers that is even close to the lands AB's don't mind a jump I usually start at sammi oal for the cartridge and work from there. If you have some do not overlook H-1000 it just might give you the groups you require you might give up a skitch of velocity with the 160 but not much. I would ask what primer you are using with the retumbo? as a primer change might just do it.

 

[Oldtrader3]

My 7mm Rem Mag (Mauser) likes 66.0 grains of IMR 7828 SSC and 160 Partitions. Velocities just over 3000 fps, sub MOA groups and a little cratering. Each rifle is different! It sounds as though 70 grs of Retumbo is working for you with the 160 AccuBond, without excessive pressure.