Home Forums Hunting & Shooting Ask The Gunwriters Long throat 7mm

I'm sure this has been discussed before but some advice from someone with more experience would help, so heres the question(s)

I am thinking of ordering a Tikka T3X in 7MM rem. mag. and new AICS bottom metal and mags to extend the COAL out to 3.6"
and throat reaming to seat a 175 gr. bullet base flush with the neck shoulder junction.
The question I have is - will long throating add velocity without exceeding SAAMI pressures? and if so how would the reloader know what pressures are?

It seems to me that when one exceeds max coal or the coal used in published recipes with no other changes that pressure and velocity are less than listed,
and if powder is increased to match published velocity one has reached the pressure limit for that recipe.

So my question is what is gained other than a longer cartridge? Does one feel that because the COAL is longer than spec that standard velocity can be exceeded with safe pressures?

Bob Hagel did an article on long throating a 7 mm Remington Mag many years a go in Handloader or rifle magazine. I'd start there, he wanted original Remington velocities without having to use a 26" barrel and 2 diameter bullets. in the 7mm Rem. MB

John Wooters also wrote up an article on long throating his 7mm Rem Mag, he used the 175 Partition( I think, can't swear to it) with base of bullet seated at the bottom of the neck. he just used a regular Mod 700 BDL. It easily adds 50+ fps, sometimes more, depending upon the rifle of course. Good luck to you.

I had a friend that had a long throat reamer so when I rebarreled my 7mm a few years ago, I borrowed his reamer. I was shooting the 180gr Berger.

Between the new barrel and the added powder capacity my Sako shoots 120fps faster than it did before, with better accuracy

oldmodel,

You won't know what the pressures are without some means of measuring them.

One rule of internal ballistics is any increase in case capacity results in approximately 1/4 as much gain in velocity, everything else being equal, including pressure. Seating the bullets to 3.6" overall cartridge length (instead of the SAAMI standard 3.29") result in about a 5% difference in powder capacity, a 1.25% difference in potential velocity. That's about 40 fps in loads around 3000 fps.

Thanks for the replies fellas.

I guess I'll have to determine if the extra expense and going back to seat of the pants pressure signs are worth it.

Does anyone have any thoughts on weather a longer throat would help with the 7MM's quirky pressures?

I bought the Handloader with the Wooters article off ebay as I debated long throating one for a couple years and I also talked to BobinNH on here about it as he'd done it several times. From what I recall Wootters' main claim was that it smoothed out the velocity variations somewhat. I finally decided against it as even in the best case scenario it was only promising about an extra 100fps and didn't think the hassle was worth it.

I had a BDL 7Mag that I worried with at the time (70's) too. I even gave some thought to having it rechambered to the 7mm/300 Weatherby. Its 24" barrel kept me from gambling on any real advantage in speed, plus, I had two young twin girls that seemed to "take all my money", ha. I "really" wanted a 7mm Mashburn, but it would have been even more costly at that time. I scratched all my 7mag itches later in life with the 7mm STW first, then the 7mm RUM. Both good rounds, both not even needed for the ranges I comfortably like to shoot game and the way I like to hunt. I still recommend a 7mm Mag of any kind for guys who ask me about a flat shooting hard hitting deer rifle. When it comes to elk I really feel ( I said feel) that a properly loaded 30-06 and the 7mm Rem Mag are about equal. The bigger STW and RUM can really sling those 160s and even some heavier, serious bullet weight though, but hey, nothing wrong with the Rem Mag for elk/deer combo at all, they sure are popular here in Utah!

In my long throated Dakota the 7 RM is pretty close to the 7 mm Weatherby. If chambering a new barrel it is defiantly worth while. Rechambering an existing barrel not so much unless you are also cleaning up a rough throat which in itself makes it worth the expense. Even with the longer leade I have to really stomp on it to get 3,000 fps with the 175s but 3100 is no problem with the 160s with mild but max loads. Still the rifle has to work pretty hard to out run my 280AI by much more than 50-100 fps. The AI has two inches more barrel going for it than the 7 RM.

What Tejano said.

Have long-throated the 338 WM, 7mmRM and the 280 both versions. Meh. The idear was to have xtra room for powder displaced by longer bullets in a "normally" throated rifle and the effort was well documented in print...except for pressures...but we were enlightened by notable swamis.

For me, it's just easier to simply use a case like the 7mm WB that has pressure documentation at higher levels. If nothing else, you have a ceiling. A pretty high ceiling at that.

Considering the anticipated length of some VLD bullets coming out, I had all kinds of hope for a certain LT rifle originally set-up for the 175 Partitions---but then the sleekness of some measured required they had to be seated deeper into the case anyway...

Which 175 are you looking to run? The Tikka also has a relatively slow 1:9.5 twist barrel for the really long, slick bullets unless you have elevation on your side. Honestly, once you add in $200 for the DBM, $75 for the magazine, and an unknown amount of smith work to modify the action for the longer COAL and barrel work, you've pretty much offset the advantages of the a Tikka. They're great for their price, but once you drop an extra $300 - $500 into them, it seems counter intuitive.

Also, the closer you get to the lands the higher the start pressure (resistance) will be.

The 160-8 grain bullets all do fine in the 1-9 or 1 in 9.25 factory twist. They don't give up much to the heavier bullets until way out there. Farther than I shoot normally. Its tempting to think about a rifle purpose built for the 180 & 195 grain bullets but then I might want more case capacity too like a 7x300 Win or the better designed Mashburn.

Agree on the Tikka as being good just the way it is. I have sunk a fair amount into Savages or Rugers and then wondered if I was gilding the lilly and losing the inherent benefits of the original package. It is like putting a Lamborgini styled body on a VW, it is still a VW.

I require a long throated woman, regardless of caliber.

OM

Bob in NH and I discussed this a lot a while ago. We both had our 7 Mags throated but I cant remember the specs but a 175 SBT is about 3.40 OAL and a 175 AB LR is 3.450. I have at least another 20 thou to touch but this is where the accuracy is.

With H1000 I am right at 3000 with a 24" Lilija. No pressure signs that I can detect and accuracy is excellent. I can get higher velocities with other powders but H 1000 has be a proven performer for me.

Lefty C

I bought a throating reamer by Clymer from Brownells back in about 1970. I played with my Ruger M77 tang safety.

Be advised: you really need a mag box longer than the standard 3.3inch 30/06 box to do yourself much good. Remington 700's all have a 3.6 inch box and give you more room to tinker. You need a extension for your throater, and a couple of brass collars to put on the extension to adjust it slowly. Put the throater to the lands, and then move the collars up until they hit the chamber's shoulder. By measuring the collars and moving them back with a fealer stock you can go slow. Work to a sample seated into an empty case.

Just oil everything up, and patch out the cuttings from the muzzle. Keep the reamer clean. I still have the reamer.

If your mag box is not over 06 lenghth You are chasing a rainbow.

[/quote]

Cut out all the drama and expense and just buy a 7mm Weatherby and your problems are solved. For the cost of headaches with reaming the Remington you could buy a lifetime supply of 7mm Weatherby brass or factory ammo! Happy Trails

I agree with WAM and the Weatherby is in the Mashburn league, closer to what you always wanted.

Seating bullets farther out brings the ogival closer to the lands and actually increases pressure, seating out and lengthening the throat negates the pressure increas of being closer to th3 lands.