Severely Overbore Chartidges and short barrel life myths...

[SBruce]

Just checking in, I want to come back and read this all later when I've got time.

Don't know how to subscribe without leaving a reply.??

 

[270 Sender0]

Kirby,

Another great read, keep them coming.

I picked up a Rem 700 7mm at a G-sale and would like to work up some loads. I like the Accubonds, would the 160 work best in a stock 7mm and would the powder you mentioned be ok for an off the shelf rifle?

Thanks

Steve

 

[Fiftydriver]

ICANHITHIMMAN,

Its a standard #3 Lilja contour. The replacement barrel I have had sitting here for three years is a Lilja #5 with heavy flutes, marginally heavier then the #3 but much larger cross section so hopefully it will allow me to stretch the rifle to 1K in good conditions in the field,if not, I always have my Raptor sitting in the wings!!!

 

[MN Hunter]

Great post - Thanks

 

[Fiftydriver]

Meatyrem,

The 7mm Allen Magnum is the fourth wildcat I designed after releasing the 257, 6.5mm and 270 Allen Magnums. The 257 and 6.5mm are based on a modified 338 RUM parent case and the 270 AM uses the 300 RUM parent case.

When I designed my 7mm AM, with the urging of fellow LRH member SS7mm, I decided to stay with the theme of the Allen Magnums to produce a product that was significantly ahead of the rest of the pack in performance for its caliber family, I needed to step away from the RUM case for something larger in capacity.

I looked at the big 30-378 Wby case but in the past I had worked with this case extensively and was not overly impressed with its cost and relatively soft case design which limited the amount of pressure you could run on the case with repeated firings.

Also looked at necking down the Rigby case but that was even more expensive and a real pain in the rear to neck down to 7mm. Plus, it and the big Wby case were extremely long.

I decided that I would go with the 338 Lapua parent case because I knew how strong the case was and that it was extremely high quality. I necked it down to 7mm, and improved the shoulder angle to my AM design as well as blow out the case body to my AM taper. My design is noticably different then a full Ackley Improved design, not as extreme in shoulder angle but close and not quite as square in body taper. I had tested different body tapers and came to realize that there is a limit to min body taper as the cases increase in size and especially diameter. You need a certain amount of taper to get good extraction with high pressure loads.

As such, the result was a case design that offered around 10% more case capacity then the 7mm RUM but also in addition to that, a case that can easily take 70,000 psi and never have a problem with loosening primer pockets. The RUM will start to get loose primer pockets with anything much over 65,000 psi.

Comparing performance,when I started I was offering the 7mm AM in modified Rem 700 chrome moly receivers. On this platform, the 7mm AM would offer legit 150 fps more velocity with same bullet weights and barrel lengths then the 7mm RUM and generally do this with longer brass life.

I have since stopped offering the AM in Remington based rifles simply because the Lapua parent case has the ability to take pressures far over what the Remington was designed for. If you load to my recommended velocity ranges, there is no problem at all but the Lapua case will take much more pressure then this without showing pressure signs and the inexperienced shooter can get into serious trouble quickly.

As such, I stopped offering it in anything except custom rifles based on receivers designed for the Lapua case size. In a full custom rifle based on a BAT, Stiller, Nesika or my Raptor receiver, you will see a solid 200 fps advantage over the RUM in same rifle specs.

Many have asked how I get this with only 10% increase in case capacity, simply put, the Lapua will handle more pressure. The RUM should be loaded in the 62,000 to 63,000 psi range for top performance and acceptable brass life. BY that I mean at least 4-5 firings per case. The Lapua case can easily take 68,000 psi and not have any problem at all. This is another reason I decided to stop offering the 7mm AM in Rem 700 based rifles, simply to avoid high pressure load data to be used in them.

Again, it will not destroy a Rem 700 based rifle but over time, its more stress then one should impose on that receiver.

Performance wise, in this 26.5" long barrel, here is what I have gotten, again, these are not red line loads, just good top end pressures:

140 gr Accubond......................3600 fps
160 gr Accubond......................3414 fps
175 gr SMK.............................3308 fps
180 gr Berger..........................3298 fps
200 gr ULD RBBT......................3210 fps

In one of my medium or heavy rifles with 30" barrel length you can add 100 fps to those number pretty easily IF the bullets will handle that velocity increase.

Its a significant improvement over the 7mm RUM but its not for everyone or for every situation but when used in its intented use, its impossible to beat. Its easy to load, very accurate and extremely powerful. Formed brass is available from me so there is no need to worry about case forming or fireforming unless you want to do that.

Hope this helps.

 

[Fiftydriver]

MeatyRem,

I have tested the following powders with the 7mm AM and a variaty of bullet weights:

RL-25
Ramshot Magnum
Retumbo
H-US869
AA-8700
H-870
WC-860
WC-872
H-50BMG (not compatible because of powder bridging issues)

Rl-25, Magnum and Retumbo work best with bullets 180 gr and lighter, the slow ball powders will work well with all bullet weights but are better suited for the 175 and heavier.

 

[Fiftydriver]

270 Sender0,

The 160 gr will work great in any 7mm chambering but works exceptionally well in the larger 7mms such as the Rem Mag, STW and RUM. Not sure which 7mm you have so here goes.

For the 7mm Rem Mag, you would be hard pressed to do better then RL-22 or H-4831 for a powder choice.

In the STW, H-1000 and RL-25 work very well. Retumbo can work very well also but you will generally get better velocity with H-1000.

In the RUM, I would use Retumbo first and formost.

 

[Boss Hoss]

Kirby-----Good Post! Something I have known for many years! The bore scope does not lie!!!

People spend a lot of money just because they THINK a tube is shot out or close to it!

Still many old "wives tales" out there LOL.

 

[Fiftydriver]

Boss Hoss,

I totally age. I have a pile of usible barrels sitting on the rack that the owners of the rifle insisted they were shot out. After a total cleaning and a bit of load tweaking, most of these barrels were still shooting between 1/2 and 3/4 moa, especially at longer ranges.

I have found that the older a barrel is, the harder it is to shoot really tight 100 yard groups with them but at longer range they can suprise you at how well they still shoot. My theory is that the older barrels just influence the bullet more and it takes a bit longer for the bullets to stabilize completely and fly true to their center of gravity. May be up in the night about that but I have still seen old barrels that shoot nearly 1 moa at 100 yards and produce under 3/4 moa at 1/2 mile.

Go figure. A gunsmith does not argue to much about replacing a barrel, thats why there is a pile of them on the rack!!!!

 

[meatyrem]

Meatyrem,

The 7mm Allen Magnum is the fourth wildcat I designed after releasing the 257, 6.5mm and 270 Allen Magnums. The 257 and 6.5mm are based on a modified 338 RUM parent case and the 270 AM uses the 300 RUM parent case.

When I designed my 7mm AM, with the urging of fellow LRH member SS7mm, I decided to stay with the theme of the Allen Magnums to produce a product that was significantly ahead of the rest of the pack in performance for its caliber family, I needed to step away from the RUM case for something larger in capacity.

I looked at the big 30-378 Wby case but in the past I had worked with this case extensively and was not overly impressed with its cost and relatively soft case design which limited the amount of pressure you could run on the case with repeated firings.

Also looked at necking down the Rigby case but that was even more expensive and a real pain in the rear to neck down to 7mm. Plus, it and the big Wby case were extremely long.

I decided that I would go with the 338 Lapua parent case because I knew how strong the case was and that it was extremely high quality. I necked it down to 7mm, and improved the shoulder angle to my AM design as well as blow out the case body to my AM taper. My design is noticably different then a full Ackley Improved design, not as extreme in shoulder angle but close and not quite as square in body taper. I had tested different body tapers and came to realize that there is a limit to min body taper as the cases increase in size and especially diameter. You need a certain amount of taper to get good extraction with high pressure loads.

As such, the result was a case design that offered around 10% more case capacity then the 7mm RUM but also in addition to that, a case that can easily take 70,000 psi and never have a problem with loosening primer pockets. The RUM will start to get loose primer pockets with anything much over 65,000 psi.

Comparing performance,when I started I was offering the 7mm AM in modified Rem 700 chrome moly receivers. On this platform, the 7mm AM would offer legit 150 fps more velocity with same bullet weights and barrel lengths then the 7mm RUM and generally do this with longer brass life.

I have since stopped offering the AM in Remington based rifles simply because the Lapua parent case has the ability to take pressures far over what the Remington was designed for. If you load to my recommended velocity ranges, there is no problem at all but the Lapua case will take much more pressure then this without showing pressure signs and the inexperienced shooter can get into serious trouble quickly.

As such, I stopped offering it in anything except custom rifles based on receivers designed for the Lapua case size. In a full custom rifle based on a BAT, Stiller, Nesika or my Raptor receiver, you will see a solid 200 fps advantage over the RUM in same rifle specs.

Many have asked how I get this with only 10% increase in case capacity, simply put, the Lapua will handle more pressure. The RUM should be loaded in the 62,000 to 63,000 psi range for top performance and acceptable brass life. BY that I mean at least 4-5 firings per case. The Lapua case can easily take 68,000 psi and not have any problem at all. This is another reason I decided to stop offering the 7mm AM in Rem 700 based rifles, simply to avoid high pressure load data to be used in them.

Again, it will not destroy a Rem 700 based rifle but over time, its more stress then one should impose on that receiver.

Performance wise, in this 26.5" long barrel, here is what I have gotten, again, these are not red line loads, just good top end pressures:

140 gr Accubond......................3600 fps
160 gr Accubond......................3414 fps
175 gr SMK.............................3308 fps
180 gr Berger..........................3298 fps
200 gr ULD RBBT......................3210 fps

In one of my medium or heavy rifles with 30" barrel length you can add 100 fps to those number pretty easily IF the bullets will handle that velocity increase.

Its a significant improvement over the 7mm RUM but its not for everyone or for every situation but when used in its intented use, its impossible to beat. Its easy to load, very accurate and extremely powerful. Formed brass is available from me so there is no need to worry about case forming or fireforming unless you want to do that.

Hope this helps.

Thats very impressive! Great information. And I thought the 7 RUM was impressive so I just had to get one. I have not been able to start loading for the the 7 RUM yet but I am itching to start. I only have it in a standard BDL with a 26" bbl but its still one of my favorite rifles. I am curious tho if you had any load data for the 7 RUM or maybe a couple of starting points. thanks in advance for any info. meatyrem

 

[meatyrem]

MeatyRem,

I have tested the following powders with the 7mm AM and a variaty of bullet weights:

RL-25
Ramshot Magnum
Retumbo
H-US869
AA-8700
H-870
WC-860
WC-872
H-50BMG (not compatible because of powder bridging issues)

Rl-25, Magnum and Retumbo work best with bullets 180 gr and lighter, the slow ball powders will work well with all bullet weights but are better suited for the 175 and heavier.

Thanks again for the info. I was thinking of the Retumbo and the US869 with 160 accubonds. Do you think there might be one powder that may be better than the other or should I try some of the others that you had mentioned? For the 7RUM in a 26" bbl stainless bdl. thanks again for any help you may be able to send this way. Meatyrem

 

[Fiftydriver]

The 7mm RUM is a great chambering. It gets a pretty bumb rap for being tempermental but I have never found that to really be the case when loaded properly, at least not on one of my custom built rifles. Remember that these big cases always perform more consistantly the more bullet weight you can put on top of them so forget bullets much lighter then 160 gr and you will be much happier.

Go to Cartridge Loads - Hodgdon Reloading Data Center - data.hodgdon.com

They will have all the starting loads you will even need for a factory RUM.

 

[340Shooter]

Hi Kirby,

I have a M70 Laredo in 7mm STW and was wondering what you would suggest for bullet and powder to start load development with?

Thanks
Ian

 

[Fiftydriver]

340shooter,

What do you want to shoot at with the rifle? Hunting, target, just long range plinking? Let me know,