Home Forums Reloading Big Game Rifles Velocity Issue

I have posted similar questions. I have a Remmy 700 KS 7mm rem mag. Everything I shoot through this gun seems very slow. I loaded up some 168gr Berger VLD hunting bullets with 65.3 grains of IMR7828ssc which is supposed to be around 3000fps. My gun with a 24" barrel is pushing them at 2730fps. I have tried some Federal Ble box 175gr and they were only going 2650fps and some handloads 140gr accubonds that the book said 3250 and I only got 3029fps. Now this gun is EXTREMELY accurate, but very slow. What are some things I could check for or do to possibly gain some velocity? At this point it is not worth lugging around a magnum or using all that powder when I can get better performance out of a 270, 280, or 280AI. I already own a 270 that shoots 140gr bullet at almost 3100fps.

IME 65 is a light load and think you could give it more gas. But, it looks like you've just got a plain slow barrel.

Dober

With the 65.3 grains I am getting an extractor mark and it appears to have flattened primers as well. But the bolt lifts easily.

might just have a tight bore i have heard about guys lapping a little or using the tubbs bullets to clean imperfections out and gaining some velocity but i don't no if it would change the accuracy

Have you tried any other powders such as Rl 22 or Rl 25? In some instances I have velocities to improve with fuller cases ie; case density.

Sometimes muzzle blast will alter the readings.
Back off another 8-10 feet and see if the readings go up.
Good luck!

Seen it plenty of times,and not just with the 7RM but other cartridges as well..... as a general trend, and there will be exceptions all over the place ,IME Remington 7RM barrels are likely tight,throats short...this is as it should be because Rem barrels are rightfully throated for Rem ammunition.....and tight barrels might be easier to get to shoot well.....but all these little things add up and MIGHT give you velocities below the potential of the cartridge,just as you are experiencing.

Anyway what I would do and have done and seen done with friends rifles is as follows.You are stuck with tha bore and groove diameters of the barrel, but not the throat. The Remington action will easily take a longer OAL than the 30/06 length commonly used because tha action is H&H length.

I would seat a 160 Partition in a dummy case so that the base of the bullet is even with the base of the neck of the case.This OAL will fit the Rem 700 action magazine easily IIRC.Then I would give it to a good smith and have the throat let out for normal bullet/land ratio with that OAL.Opinions will vary on how much velocity increase you will get,but IME you will get some;and you will not hit the "wall" you are experiencing with manual loads as soon as you do with standard factory throats.

Some will say that the rifle will not shoot,and this is not necessarily true;like any other rifle, it will like some bullets and dislike others.

The other thing I would do is get off the 7828(which is an excellent powder for the 7RM,and I use it myself),but in this case I would go to a double base powder like R25,which has somewhat more powder energy,and may give higher vels.Some other slower powders like H1000 may give great results also.

I would not let temp sensitivity trouble my head because I would test the loads in both hot and cold weather(which is what the chronograph is for),and shoot the rifle to determine if there is a difference in POI,vel, etc,rather than just assume it is going to happen.

Hope this helps,and good luck

I have run three different 175 factory loads through the chronograph in 4 different 700's with one a 26 inch Sendero, they all three ran right around 2750 none broke 2800, I run 168 Bergers over 73 grs of Retumbo for right around 3050, average for several 700 7mags, maybe give that a try and see where you are, I havent reached the velocties listed in the Nosler books except for the 140's and RL22, I used to shoot 160 Sierras over 71 grs of 7828 for @ 3100 a load out of Finn Aagards book, with no real pressure signs but didnt mike the web, shot well also.

+1 on Bob's comments, depending of course, where the throat is at now.

I've easily gotten 3170 out of 3 different 7 mags throated to the 160 Partition as Bob suggests, using RL-22..........I personally think '25 is a touch too slow until you get to 175 grain bullets.

W/o having the gun in hand to see what's going on now with it as is, it's hard to say this, but lots of book 7 mag data is woefully conservative, IMO.

I'd be looking very carefully at all components & the rifle to try to determine where you're really at, pressure wise.

FWIW

MM

What Dakota kid and MM both say is equally true.

I have a 7 mag here that has a more or less standard throat on a Douglas tube that gives very "7-maggish" velocities without any trouble,but does so with loads a couple grains below max; for example some data will show 70 gr RL25 as max with some 160 gr bullets;this barrel gives almost 3100 with the 160 Partition and 68 gr RL25.

66 gr IMR 4831 gives 3250 with 140 AB's amd Partitions....these are not hot loads but the velocity is there.

So every rifle can be a law unto itself....but not really unusual as I have seen much the same things with the 300 Win Mag and standard throats as well.

It's been a long time since I bought any store ammo but traditionally they are considerably under what they post for velocity. You should have seen what some of the velocity claims were back before every kid on the block had a Chrony.

I think you can juice your load up a bit without a problem. Try loading up only one each of the additional powder loads until you get to max and see how each one looks and feels. One round won't give you a complete picture but you'll have an idea and you won't have a lot of ammo to tear down if the loads are indeed too hot.

My 7mag is wonderfully accurate and I've killed a lot of stuff with it but I've never Chronied my hunting load. (maybe I don't want to know what I'll find out)

..............If you`re going to own a 7mm mag, then you should have one that performs almost or on par like most of them.

With any rifle maker there are slower and faster barrels, not so tight and tighter chambers and different throat specs. In your case it appears you have a tighter bore and maybe a variance in the throat specs. The style of bullet ogive also makes a velocity difference. The Berger VLDs will generally have less bearing surface that touches the bore than do most bullets, so your lower velocities using them is somewhat surprising.

To reduce the bullet resistance as its traveling down the barrel, maybe a gunsmith (if it can be done), could shave your bore lands down another 1/5000ths (guessing; or whatever) of an inch and change the throat specs a little. Will that affect your present great accuracy? I don`t know!

In looking in my 49th Edition Lyman manual, I read that using 66gr IMR7828 behind a 168 gr Sierra HPBT from a 26" barrel gets 2870 fps @ 52,000 CUP as a max loading with a COAL of 3.290". At 2730 fps from your 24" er and taking into account your 2" of shorter barrel length (about a 50 fps loss), your running about 90 fps behind the Lyman example assumming their velocity with a 24" er would be around 2820 fps. But wait! You`re running 65.3 grains (7/10ths less). So deduct about another 40 fps which would bring Lyman`s example down to about 2780 fps if they were using 65.3 gr IMR 7828 from a 24" barrel. So you`re running about 50 fps behind Lyman.

On the other hand, from my Sierra Edition V manual, I read that using 66.4 gr IMR7828 behind the same 168 gr Sierra HPBT from a 26" barrel gets 3000 fps with an additional 4/10ths of a grain over Lyman; (an additional 20 fps or so with an extra 4/10ths of a grain). Assuming Sierra were using just 66 gr from a 26" er, that would bring it down to about 2980 fps, with an additional minus of around 50 fps or so for a 24" barrel, bringing Sierra`s findings down to about 2930 fps or so using 66gr from a 24" barrel. Then calculating about a 40 fps additional drop (the 7/10ths of a grain less you are using which is 65.3 gr), that brings Sierra`s example down again to around 2890 fps if they were using 65.3 gr IMR 7828 with a 24" barrel. In the Sierra example, you are still running even more behind at about 160 fps.

With your individual rifle and from your 24" barrel, I think your velocity expectations might be just a little too high at 3000 fps. Combine that along with a tighter bore, you can easily swing 150 fps in a non-favorable velocity direction.

IME a long jump to the lands leads to lower velocities. How much of a jump do you have?

Don't feel bad, I have winchester M 70 270 wsm that will not safely hit 3000 fps with 150 gr handloads, 3250 with 130 gr grainers. I have tried five different powders with these bullets, factory winchester 150 gr loads run 3090 fps, however all of the handloads shoot under 1 inch groups.

Low velocity is commonly a result of low pressure.

Could be one or more of many factors.

-bore diamter
-chamber volume
-brass volume
-throat length
-seating depth
-powder variation
-primer intensity
-temperature

I'm sure there are others, but those jump to mind.