Action Fluting/Scalloping/weight reduction

[ntsqd]

Tried a search and didn't find anything on this. Build is a Howa Mini LW bbl in 7.62X39, goal is under 5 lbs. scoped and slung. Probably not going to get there, but that's the goal. Obviously not a LR precision rifle, more of a CA A Zone "Hiking up steep hills with a rifle" sub 300 yd. rifle. Not a lot to work with in this tiny action, but it already has a hollowed-out Boyd's on it (forearm shortened ~2" for esthetics), Leupold 2-7x LW in Talley AL mounts, and Ti action screws because I could (https://monsterbolts.com/products/6...orx-button-head-caps-screws-iso-7380-din-9427). It's at about 6.5 lbs. now, which is why I doubt that I'll reach 5 lbs.

The barrel is a pretty light profile now and as best as I can infer is the original design length for the cartridge. I'm more than a little hesitant to flute it, but I know I could find another couple ounces by doing so. Same with shortening it, that's just not going to happen as I like the esthetic balance of barrel length to forearm length that I have now.

However, There is some meat in the action that I suspect could be fluted/scalloped/thinned w/o grossly affecting the action's rigidity. Obviously the front bridge is off limits. As is the scope mount region of the rear bridge. What about the sides of the rear bridge? What about the squared-off flat belly of this action where there isn't a pocket for the mag? It is about to get pillered so I don't need that flat belly. Anyone done this sort of thing or had it done? I'm down to a war of ounces, a little here, a little there, etc. I have kidded about drilling those Ti action bolts......

 

[jd5521]

I would not recommend fluting the action at all. IMO you would not shave near enough weight off and may compromise the structural integrity of the action when firing. Best bet is lighter stock, lighter scope and/or carbon fiber barrel depending on what your existing barrel actually weighs.

 

[ntsqd]

Scope is the lightest that I know of, which isnt' saying a heck of a lot. Maybe it could be lighter, but I suspect that a quality 8.5 oz. 2-7x scope is going to be hard to beat. Talley says 4 oz. for their rings.
Brownell's says 3.6 lbs. for the barreled action, with polymer bottom "metal" and a polymer magazine.
That's 4.38 lbs for a scoped, barreled action. That's about what I recall my scale saying.

Stock is about as light as I can get it without compromising it's integrity. there may be a little to be found in the forearm, but I'm getting close to making it flimsy. As it is even if it fit there's no way I'd bolt this stock to a magnum, it won't take it for very long.
Last that I looked there is no composite stocks made for the Howa 1500 Mini, 1500 SA/LA yes, but not for the Mini. The OE polymer stock doens't count for anything. One or two stock makers were willing to consider it if I sent them my barreled action for them to make a pattern off of. Lead times were way out there (year, maybe more) because of the more popular actions in line ahead of it and we never got to talking about price.

Being overly general I'd say all of the action's strength is in the front bridge and about 1/2 of the accuracy is in the rear bridge. So if mass can be thoughtfully removed from the rear bridge and bottom of the action in a way that retains most of the action's stiffness while removing some mass I don't see a problem with it. Not too long ago a fluted barrel was considered an "Elmer Fudd" looking for a place to happen. Now look at them. The question is, can it be thoughtfully fluted or scalloped or thinned, or is it about as light as it can go?

 

[jd5521]

I think the recoils forcing back into the bolt could strain the rear of the action. Just my opinion but the energy of everything is forced rearward once fired.

I don’t know what your current stock weighs but bell and Carlson make a stock right at or under 2 pounds.

 

[stilesg57]

I’m impressed by your commitment to building a lightweight. My mountain rifle is a Howa lightweight mini in 6.5 Grendel with the factory stock, Talley LW rings and a ~12oz Leupold 4-12x40ao scope. Under 6.5lbs with 5 rounds in the mag. Pretty happy with that considering the cost of the rifle and lack of custom work/parts.

 

[ntsqd]

This IS new: https://www.bellandcarlson.com/index.cfm?fuseaction=category.display&category_id=1139 Thanks for the pointer!

Weighed the much-modified Boyd's laminated stock last night late; 2.1 lbs. Whole rifle is 6.4 lbs. less any sling or studs. That's really not all that bad, I just want to see if I can get it lighter. The back-story behind this rifle speculated that it could be 5 lbs., so that's my goal. With a Woodruff Key cutter I could probably get the stock under 2.0 lbs, but not by a lot before the forearm becomes flimsy.

My "mental FEA" assumes squared-lapped lugs (within what can be done with the barrel still in place, I did). Those take all of the combustion thrust within the front bridge. With no fore/aft mating surfaces at the rear, all of the thrust has to be at the front.
Recoil is a bit different. Due to the eccentric mounting method there is some moment about the recoil lug. Again, my "mental FEA" shows the action trying to bend concave up while under recoil (assuming a perfectly rigid stock and a 'normally' rigid action). Temper that with this is only a 7.62 X 39, not a .375 Cheytac. Prudence is good as its safe, but being realistic is also important.

Maximum strength will occur with the outer fiber being as far away from the center-line of the action as is possible. Unfortunately Howa pocketed most of the bottom for the magazine, so a great deal of those outer-most fibers in the flat belly of the action don't stretch from mounting screw hole to mounting screw hole. What remain got notched for how the trigger assembly is located. Without detail modeling the action and running it thru SolidWork's internal FEA I'll estimate that most of what's left in the flat bottom is just weight. It could be rounded off ala an M700 et. al. and not loose any strength or rigidity.

That OE stock must be crazy light. I'm assuming that the 6.5G has the same barrel profile, so your barrel should be slightly heavier. That you're in the same weight range with a full mag is impressive.

 

[stilesg57]

It’s lighter than a Hogue, but not SUPER light. Damn, I just had it off a couple weeks ago while fiddling with the trigger weight, I should’ve weighed it.

With ~4oz less in the scope, no rounds in the mag, some more aggressive stock inletting around the barrel and the swing swivels removed, I think you could get to the magic 5.99lbs unloaded before having to flute any action parts.

 

[ntsqd]

No swivels in place now. I'm going to moving to MSR type swivels as I just like them better & I think that Mike would approve. One in the stock toe, one on each side of the forearm near the tip, and a traditional stud in the traditional forearm location for any potential bipod use.

Fellas on another forum put me onto Kampfeld and Twisted Barrel for action fluting, so I've sent both an inquiry. Marty Kolbet from Twisted got back to me suggesting instead going with an MPI stock. I've an inquiry in to them asking if they inlet for the Howa Mini. If they do, their ultralight stock is a claimed 10 oz.! That alone puts it under 5 lbs.
Another guy suggested a Manners EH4 stock, but they don't inlet for the Howa Mini.

 

[stilesg57]

Daayyyyuuumm let me know about that 10oz stock situation when you find out!

 

[brianf]

if you dont mind the look and are out of options start drilling holes in the stock

get a big hole saw and chop out a chunk of the butt

mill down the bolt handle to a blade style

you can flute barrel but when they get warm they wander more and more eratic, and you really wont save much at all.

i actually stopped doing it in general

dont touch the action, 2 oz isnt worth a bolt through the face

 

[ntsqd]

Will do.

....
My "mental FEA" assumes squared-lapped lugs (within what can be done with the barrel still in place, I did). Those take all of the combustion thrust within the front bridge. ...... Temper that with this is only a 7.62 X 39, not a .375 Cheytac. Prudence is good as its safe, but being realistic is also important.

I'm not worried about or interested in compromising the action's strength. The front ring is hands-off. Everything to the rear of it is not load bearing in terms of the bolt getting loose. Cutting on the rear bridge may compromise accuracy and obviously I'm not interested in that, but some of the metal appears to just be mass along for the ride w/o doing anything for strength or rigidity. As best as I can tell it is still there because removing it in a production environment would be cost prohibitive.

The butt of the stock has already been hollowed out clear up to just behind the wrist. Had to buy an extension for the spade drills and a carbide burr with an extra long shank to reach all of the way in there.
The forearm has been hollowed out under the barrel. That's why it weighs only 2.1 lbs., it weighed about 3 lbs. when it arrived.

Could drill some holes in the bolt handle, but coming from the racecar world I view holes generically as evil stress risers. Hollowing out the knob is about as far as I'd go down that track. I'll have to measure that and do the calc, could be worth an ounce or more. Holding it will be a trick, but I can fangle up something for a one-time use.

The third rapid succession round's POI moves some now. Am not too interested in fluting the barrel for that reason. If I do flute it I'll give cryo a try, see if it helps any. Worst case I have to get a new barrel fitted. I'd take that opportunity to upgrade to a premium barrel mfg. in their lightest contour at 20" long.

 

[ntsqd]

Finally talked to MPI, its going to take about $800 to stock this $260 barreled action that lightly. Hard to justify given the limited use this rifle will see. I do intend to send it off for whatever action thinning the gunsmith is comfortable with, cut the crown, and then he'll Cerakote it.

 

[stilesg57]

Yeah, rough pricing man. Diminishing returns take hold pretty fast at a certain point. A lot cheaper to go from 11lbs to 8lbs than from 6.25lbs to 6lbs.

 

[Bwells]

stilesg57, thats pretty impressive.

 

[ntsqd]

What is?

 

[FPFirearms]

The AG Composites privateer is pretty light.