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Discussion Starter · #1 ·
Hi all!

Newbie from the leftist state of Kalifornia. I have an M77 MK II chambered in 7mm Rem Mag. I want to re-barrel this gun to one of the 300 magnums. Is this action strong enough to chamber it in 300 RUM, Weatherby, or Win Mag?

I want to this to be my Kalifornia only gun (lead free). I've been shooting 135 grain Cutting Edge Raptors. The C.E.B. bullets shoot very well, so I want to build a 7mm/300? to shoot the 168 grain C.E.B. MTH bullets, or build a 300 RUM to shoot the 180 grain C.E.B. MTH bullets. Just not sure if the action is up to the task for an Ultra Mag chambering.

Any info or opinions are greatly appreciated!


Thanks, Mike
 

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The M77 Mark II long action is capable of handling the power of any of these rounds, however, it's not long enough to handle any of them except for the 300win mag. The M77MkII Long Action can only handle 3.34" Long Action cartridges, but is too short to manage 3.5-3.6" Magnum Action cartridges.

You could build any of them as a single shot, but they 300 Wby and RUM and 7STW are too long. Doing so would require you to remove the bolt to extract/eject a loaded round, and frankly, it's not a good move for the CRPF Ruger M77 action, since you'll have to drop all of the rounds into the chamber and smash the extractor over the rim, rather than feeding Controlled Round from the magazine as it was designed.

The M77 Mark II Long Action mag box is only typically ~3.45" inside, so you won't be able to feed from the magazine for any of the longer cartridges.

The ejection port on the M77 Mark II Long Action is only ~3.15" inside, with only about 0.5" of bolt face retraction behind the front of the bridge - which makes it SEEM like a 3.6" cartridge would fit, but in reality, the standing ejector makes contact long before full bolt draw, so the M77MkII Long Action just can't eject a full length Magnum cartridge.

The 300win mag fit just fine. The M77MkII was offered in 7mmRM and 300wm both, as well as 338WM, all 3.34" cartridges.
 

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I have lots of M77 MK II rifles and all of them have been re-barreled.

Generally the only restrictions are to maintain bolt face/cartridge head sizes and cartridge length as defined by receiver length as magazine boxes can be swapped out or in.

The M77 MKII action is massively strong and easily capable of handling pressures of 7mm Rem mag or .300 Win Mag loads.

But as mentioned by VT, the receiver is not long enough to handle rounds like the .300 WBY, .300 Ultra Mag and so on. .300 Win mag loads will fit inside your existing magazine.

In loading .300 Win mag ammo attention in regard to length is needed. A situation may occur if an excessively long round is chambered then needed to be removed without firing. Upon drawing the unfired round with bullet the blade type ejector will pop up and attempt to swing out the unfired round and the loaded round, with bullet, will be prevented from being tossed out because to bullet will be obstructed by the right side of the receiver ring. At this point, the bolt cannot be removed because the MKII is controlled feed and holds the blocked cartridge against the bolt face with the extractor and the ejector is being pushed against the loaded round.

The fix is to push the ejector down to allow the bolt to be drawn back and out. I have had some success by pushing the loaded round back into the magazine but the cartridge being longer than the magazine and with a tight fitting extractor this often does not work.

The .300 Win is just about the most common .30 mag because it will work in a standard 06 size action. .300 mag ammo has been faulted because the base of the bullet is often far below the junction of shoulder and case body. In practicality this does not seem to affect performance. But should your chamber allow long rounds the possibility of removing loaded ammo might be a problem. Chambering your rifle to .300 Ultra Mag would make the loaded ammo removal problem a certainty.
 

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Some more info:

SAAMI

This link will enable access to various chamber/cartridge drawings. Included in the SAAMI cartridge drawing is the COAL (cartridge over all length) and is specified as being between 3.215 and 3.340 inches for the .300 Win. this will fit inside a M77 magazine box. Observe this is the same length as specified for the .30-06.

Should you have a longer magazine box than standard, intended for 3.340 cartridges, or no magazine box, the COAL may be increased out to where a bullet may be seated to where the bullet shank ends and boat tail begins by modifying the chamber by use of a throater (cylindrical reamer). This operation will enable maximum charges of powder (in this case lots of H1000) and will usually keep the junction of the boat tail and shank just above the junction of neck and body of the brass thus avoiding the dreaded "donut". All this is sort of picky, intended for obsessive types.

Attached is a photo of some .30 rounds.

From left to right:

.300 Win Mag w. 208 Amax, COAL 3.5,
.30-06 w. 180 interlock, COAL 3.340
.308 Win w. 155 Barnes Match Burner, COAL 2.8
.300 RSAUM w. 150 SST, COAL 2.8
.30 150 SST
.30 178 AMAX
.30 Barnes tipped 168
.300 RSAUM w. 180 interlock
.30 208 AMAX
.30 180 Barnes TX

Looking at all of this the extended length .300 Win mag works real good with 208's but the short .300 RSAUM would not be good with 208's and mine is only loaded with 150's.

Loading bullets into the area below the neck is almost universal with the .300 Win and its designers did it this way to enable more powder to be put into the case.

In theory, if you wanted a more perfect .30 round that would work in a standard .300 Win mag magazine box, a long throated .300 WSM could be made up to handle any .30 bullet in a standard 06 length magazine. This would be sort of an odd cartridge, not giving good results with factory ammo or light bullets. I have lots of .300 Win Mag brass, but if I had to begin this project again I would take a look at the .300 Ultra Mag.

The standard .300 Win Mag works real well in 3.340 inch long magazines and is real popular because it works real good.
 

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Discussion Starter · #6 ·
Thanks BassMan, more great info.

I have a 300RUM for shooting lead, out-of-state hunting and it shoots so well, I don't want to burn the barrel up playing with these copper bullets. I have the M77 MKII 7mm and an older M77 270 that I want to re-barrel for this project, which will exclude the 300 RUM.

I can use the 7mm SAUM, WSM, or 7mm/300 WSM to shoot the .284/168 grain CEB bullets.

The 300 SAUM, WSM, RCM, or the 300 Dakota will work with the 180, or 190 grain CEB bullets.

I'm not sure where the returns will start to diminish...powder capacity vs. Bullet weight/length etc.

-Mike
 

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I bet you can see the level of the powder in your measure drop by big increments every time you drop a .300 RUM charge. Yes, the .300 RUM will probably eat up a barrel faster than a .300 Win.

In a re-barrel job with an older M77, pre MKII, be aware that the head size of a belted .300 Win Mag, 7mm SAUM, or 7mm/300 WSM case is bigger than that of a .270 Win, this with the plunger type ejector on the older push feed M77's, makes a conversion from .270 Win impractical. Should you need/want to use 7mm CEB bullets (I am sort of ignorant of these) you might consider re-barreling the .270 Win to a .280 Rem, or a .280 AI (Ackley improved) (Nosler version). That way you would get a 7mm that would fit and work inside the .270.
 

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Discussion Starter · #8 ·
Yes Sir! 89.2 grains of H1000, 3018 fps is where she shoots the best, somewhat mild load with 215 Bergers seated out to 4.000" COAL...shoots 1/3 moa. I thought I'd never use 8 lbs of powder in one gun until now.
 

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Seems like you're setting out to spend a boatload of money for minimal returns. Shooting a .300RUM with all leads - did I read that correctly?

Like Bass mentioned, opening the bolt face on the Ruger M77's is usually a wasted effort and expense. It's not really more complicated than opening any other bolt face, but doing so is generally a waste of money for any rifle action - cheaper to sell it off and buy the proper bolt face.

It also sounds like you simply need to decide what you really want to shoot, then pick the cartridge to deliver it. I would not consider the 7 saum or WSM to be a step up from your 7rm, frankly, they would be a backwards step. Then, similarly, there's really not a lot that the 300wm will do that a 7rm will not, unless you strap a fast twist 30-34" tube out front and run 200-220grn pills. Run 160-180grn pills at max ejection length (which matches mag length pretty well in Rugers), and be happy.

Similarly, for the .473" standard bolt face .270win, there's just not that much to be gained by spending money to convert it to match your other rifle, as it would do exactly that with the 7wsm or saum or 300wm. My wife and I have hunted for years with 7rm and 300wm rifles, there's really not enough gap between them that I'd ever spend $400 to re barrel 7 to 300 unless the barrel was already shot out.

There is no replacement for displacement. The long action 7rm and 300wm magnum cases essentially maximize the long range potential of the long action magnum bolt rifle. Short action magnums are near, but when the legs get stretched, they don't exceed the long action versions, but do tend to have accelerated throat erosion, poorer feeding, and poorer case life. A 7wsm Savage custom is one of my favorite rifles, but I'd still rather have a 7rm for long range killing over the WSM. For paper, the lighter recoil of smaller cartridges is nice - which is why I bench a 284win at 600-1200yrds most often.
 

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Been there and done that with the short mags. I have a .300 RSAUM that I shoot 150's out of but see little advantage over my .30-06 except 1/2 inch shorter action length. I would not go there again. Brass is real pricey at $2.50 - $3.00 per piece for .300 RSAUM and .300 WSM, I had to have one of those also. I get about 200 fps more than a 06 will with 150's and less difference with much longer bullets like solid copper Barnes types.

If I read this correctly solid copper, no lead core bullets are to be used like in "Kalifornia".

My .300 Win mag has a 26 inch 1-10 twist barrel and being a single shot, no magazine, push feed, can handle 3.5 COAL .300 Win mag rounds loaded with lots of H1000 powder and the 208 grain Hornady Amax bullet. Application of a .30 throater after chambering made the 3.5 COAL possible. These just won't work in a standard .300 WM magazine rifle.

Despite, the 1/2 inch longer action length and short neck and bullet encroachment into powder and belt; I would go for the .300 Win Mag having a COAL of 3.34 inch over the .30 short mags with a COAL of 2.8 or so.

Because of a number of reasons I would not go for any short magnum. I have a 7mm RM and .300 WM in the event my small 6mm's (.243, 6mm AI) and 6.5 mms (6.5-06, 6.5X47 Lapua) don't have enough killing power.
 

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Discussion Starter · #11 ·
Varminterror, lead bullets is reference to typical cup/core (copper jacketed lead core bullets). My error assuming everyone would know that California is in the later stages of outlawing the use of lead for hunting purposes. A large portion of the central valley and surrounding mountains is a "no lead zone" and has been for a few years now (supposedly to protect the endangered California Condor from lead poisoning). in 2016, lead is also banned on State and Federal lands and hunting upland birds (except quail & ?). by 2019, all lead ammunition is banned for all hunting purposes. This creates a different challenge for hunters, simply because lead-free copper bullets are different in sectional density and form factor, than lead core bullets of equal caliber and weight. Traditional twist rates don't usually stabilize the longer copper bullets well. Most folks are having a hard time getting any of the monolithic (copper) bullets to perform like what they are used to shooting. My MKII might satisfy some folks, shooting 3" 100 yard groups with copper, but I am not... The older M77 270 is even worse. I suppose I could sell them and buy a new gun, but new factory rifles aren't typically built with the faster twist rates needed to shoot longer by caliber/weight bullets. Additionally, Rugers are difficult, if not impossible to extend the magazine length to accommodate longer cartridge configurations. I like Rugers; my first deer rifle was a tang safety 270 that shot "lights out" with hand-loaded Ballistic Tips. I will either re-barrel the 7mm to a faster twist or change the cartridge to something that will allow a longer COAL.
 

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Ah - my apologies... Lead CORE bullets, not lead bullets... I have the luxury of not living in a communist country, so I'm not forced to live by misguided and irrational law, so when someone says "lead bullets" to me, I don't assume that they meant "lead core, copper jacketed bullets". I assume they mean what they say - lead bullets...

Based on your last post, I'm not sure you're understanding what Bassman and I are saying:

You can't go longer than 3.40" in your action. Your RIFLE is the limiting factor. The last line in your last post indicates that you're missing this point - there is no cartridge that "will allow a longer COAL" in your Ruger M77 Mark II, the RIFLE will not allow a longer cartridge unless you remove the ejector and convert it to a single shot.

As such, your only "faster" options for 3.4" compatible cartridges are 7mm-300 and 7mm Dakota, which aren't going to be fast enough to make a difference. If you really do have a velocity vs. twist rate problem, then neither of these will gain enough speed over the 7mm RM to make a 9.25" twist work.

Since my first name is Dakota, I built a 700 in 7 Dakota, the gains there are minimal - and based on the data from CEB, you'll need a fast twist barrel anyway, so the end solution is the same - a faster twist barrel - but you'll spend 2-3x more on brass and more on dies, with no real benefit.

Personally, I'd throat out that 7mm to accept long seated bullets to fit your maximum mag box - matching it up to the CEB bullet weight you want to shoot, and work on my seating depth.

I've shot a lot of all copper bullets over the years, CEB's included. They don't follow the same rules for ideal COAL as conventional lead core bullets, and I've seen a lot of reloaders make the same mistake that I made on my first foray into copper solids - you don't seat them the same as lead cores, they like a little room.

Your twist rate is likely the issue - and you won't be able to speed up enough to fix it. Even with a RUM case, you won't get enough speed gain. The CEB site suggests a 1:7.5" "or faster" twist for their 180 and 195grn MTAC and MTH. I'm not sure it'd need to be that fast in a 7mmRM case, but a 9.25" standard twist won't cut it. I'm calculating an 8-8.5" twist for these bullets.

However, in running the numbers, you'd have to get over 3600fps for a 1:9" to stabilize these bullets - which the RUM, STW, Dakota, and others just won't do.

So I'd either pick a different bullet, different bullet weight, or strap on a faster twist barrel in the same 7mm RM. All of your other cartridge options will either have the same problem with twist rate, or won't fit in the rifle action.
 

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Discussion Starter · #13 ·
No worries! You and BassMann provided a lot of good info that would have taken a long time for me to assemble. I think I'll keep shooting the 135 Raptors so I can magazine feed them, until I re-barrel. The plan has always been to put a tighter twist on the gun, I just wanted to see if there was a cartridge combo that would let me shoot the heavier/longer bullets from this gun, without losing too much velocity. I think we have debunked that thought. I think I'll go ahead and try the 180s in my RUM to see how they shoot.

I didn't know that single feeding a cartridge in the MKII was a bad idea, I've been doing that for a while now with the longer bullets.

Any way, I appreciate the thought and effort!
-Mike
 

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Discussion Starter · #14 ·
Varminterror and BassMan,

I "mis-spoke" in the earlier post(s): "change the cartridge to something that will allow a longer COAL."

What I meant say was, change the cartridge to something that will allow me to use a longer bullet and stay within the max COAL for this rifle.

Sorry for the confusion!
 
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