7mm Bore Rider designs

[Iron River Red]

I want to give a bore rider a try in my 7 BR. Any suggestions, comments or concerns.

I'm looking at a gas check design and have slugged the barrel.

Dimensions are: .2837" groove diameter and .2754" land diameter w/1:11" twist

135gr

Is bearing length good or bad for accuracy and velocity?

Should the nose be a certain ratio to the amount of bullet inside the case? I'm looking at more nose/front band length to compensate for freebore...

Should the base for the gas check be kept to a minimum or does it matter?

Using Dan's mold design software I have some nice looking combinations, but I'm still new to some of the terminology and its effects on accuracy.

[Pb head]

Try RCBS 145 Sil , hear tell it's accurate. Seems like a lot of the XP 100 boys use the Seaco #71 160gr tapered boolit

Pb head

[Buckshot]

............I likw the RCBS 7mm-168. From alloy a bit harder then ww my mould drops them at 172grs. I've shot it to a bit over 2400 fps from a Brazilian M98/08 and a 1897 Rem RB (both 29" barrels).

Most generally a longer bearing surface on the slug ensures being well guided.

Theory has it and it may be true for ultimate accuracy that a bore rider is supposed to do it's best when well supported by the lands. The most support obviously comes from the war expedient 2 groove barrels. Least from the Mauser-Springfield type of 4 narrow lands and 4 wide grooves.

In these narrow land types, a Loverin is supposed to work best. There is one thing about a bore rider though, and that is it is sensative. It must guide at the minimum on the lands, otherwise it may travel down the barrel tipped and so exit tipped. I like to see bore riders actually engrave a bit.

..............Buckshot

[Bass Ackward]

[QUOTE=Iron River Red]Is bearing length good or bad for accuracy and velocity?

Should the nose be a certain ratio to the amount of bullet inside the case? I'm looking at more nose/front band length to compensate for freebore...

Should the base for the gas check be kept to a minimum or does it matter?

QUOTE]

IRR,

Bearing length is everything to lead. There are always exceptions, but keep the nose short. I prefer no more than 25% of bullet length to be unsupported. 80% bearing length is always my goal. So on lighter designs, I go the 80% and the heavier I might scrimp at little.

Ratio in the case? No. But if you think you might have a chance that the GC is going to enter the case then keep your GC groove fairly narrow. But if there is no danger of this, open it up to push the first band up away from the pressure without going over board. I like about .120 shanks on rifles.

Filling the throat length is great. But why a .... solid band? What does it hurt if you have unfilled lube grooves exposed? The more lube grooves the longer the bearing area for the same weight bullet.

The more lube grooves the less front heavy the bullet.

Or .... the larger the percentage of weight on the back of the bullet, the easier it is to stabilize.

Or .... the better / more accurate it will be at longer range.

Take your pick.

[7br]

Just out of curiosity, what are you shooting this in?

[StarMetal]

My Sako 7mm-08 carbine loves the Lee 135 gr. It shoots it at both low velocity and very high velocity (2700 fps) under an inch at 100 yards. I bought it because the 7mm-08 have a very short throat and my Sako doesn't have any freebore to speak of.

Guys I think Iron mentioned 135 gr in his post, although he didn't mention the type of firearm he will be using. I assume a TC Contender.

Joe

[Iron River Red]

Yes. 135 gr in a 15" Encore with a 1:11" twist.

[7br]

I shoot the 7br in a 10" encore. The 145 RCBS borerider fits pretty well. About 18.3gr or so of IMR4227 will give you about 1700 fps. Accuracy as I recall was pretty good. I haven't shot it for a while.

[jpb]

My Sako 7mm-08 carbine loves the Lee 135 gr. It shoots it at both low velocity and very high velocity (2700 fps) under an inch at 100 yards.

Joe

Hi Joe

I have the same mold -- could you post what load and lube you are using for 2700fps?

I'd love to have one fast load for practice on moving targets at the range!

jpb (in Sweden)

[Buckshot]

............JPB, a hearty welcome to the board. ANOTHER Swede! :D

"It shoots it at both low velocity and very high velocity (2700 fps) under an inch at 100 yards."

I'd like to know too, and the twist, alloy, primer, etc.

.............Buckshot

[jpb]

Thanks Buckshot!

I've been lurking for quite a while, but have just been reading and learning.

Here in Sweden most ranges have a life-sized moose target that is pulled along rails (at realistic moose running speed!). This is shot at a little under 100 yards. Lots of fun!

For the 7mm Rem Mag, I have lots of nice low-recoil loads at moderate velocity, but for the moving target one really needs something at least 2500fps to minimize lead errors. 2700 would be even better. I want the velocity to be similar to my hunting loads so that my leads will be the same of course.

So far, I have found no high-velocity load that will do well with cast bullets in the 7mm Rem Mag.

Once I find a good high velocity load, I think I may run into another problem. One must shoot 4 fast shots at the running moose target, so the barrel is getting hot by the last shot. In the past that seemed to make leading worse, but I'm not sure if this is a general phenomenon. Comments?

I also shoot cast in my.358 Norma Mag, and my .375 H&H Mag. For these, I have lots of high velocity loads, but a suitable lube is still a problem for me. What lube is good for 2500fps to 2700fps?

I was thinking of trying a double coat of Lee Liquid Alox, or I will likely have to make my own lube. I've heard good things about high velocity and Rooster lube, but ordering from the US is likely to be difficult because many US companies won't bother for an order which will be under $20.

Cheers from Sweden,

jpb

[StarMetal]

jpb

Well I have to did up the number of grains of 4350 powder I use in that load, but that's the powder. Buckshot knows very well what I was shooting. Like I just mentioned, 4350 powder and the 135 gr Lee and I used my double gascheck method. That is a gascheck on the bullet in the normal fashion, then a sized gascheck inverted and placed in the mouth of the case and seated along with the bullet. BE SURE you DON"T seat the loose gascheck below the neck!!!!!! It will fall into the powder then. One more thing, this 2700 fps was shot with my own lube by the way. I made this fine lube and also my bubble gum lube which Bass Ackwards loves to chew so much.

Joe

[Bass Ackward]

For the 7mm Rem Mag, I have lots of nice low-recoil loads at moderate velocity, but for the moving target one really needs something at least 2500fps to minimize lead errors. 2700 would be even better.

One must shoot 4 fast shots at the running moose target, so the barrel is getting hot by the last shot. In the past that seemed to make leading worse, but I'm not sure if this is a general phenomenon. Comments?

What lube is good for 2500fps to 2700fps?

I was thinking of trying a double coat of Lee Liquid Alox, or I will likely have to make my own lube.
jpb

jpb,

Glad you decided to post. Lot's of good cast loads huh? I especially like to hear that. I was almost drumbed off the board once because some people believe you can't shoot cast bullets in a 7MM Mag. Strange huh?

Now I have never done HV in a 7MM Mag specifically so I can't give you a load. But the process has worked in everything else so far. It is actually is a superior method the more over bore the case designs. The method is high velocity, but with low pressures. Use powders that achieve a 90% loading density and produces about 34,000 psi maximum. Then seat into the lands for ignition. The 34.000 figure I listed was for air cooled WW and a strong, lighter weight bullet design. (no bore riders). Pressures can of coarse go higher with a harder bullet.

A good guess for a powder that you might be able to obtain would be RL-25 and about a 140 bullet weight or less. The heavier the bullet, the slower the powder you have to run and visa versa.

The liquid Alox is always good for a base coat for bullets intended for HV because it won't melt. When dry, fill the grooves with some other lube though. Between the two types of lube, you should be good to 2700 fps as long as you use the slow powders. Work up your loads as you will shoot at the range. Understand the concept?

You will know right away by the target. The type of the secondary lube you "require" will be based more on the lube carrying capacity of your grease grooves than anything else. But something you could make is the Felix lube at the top of this section. Would work like a charm and you can taylor the amount of lanolin for either a less or more slippery consistency based on what you need for your bullet velocity and hardness. But I think almost any lube can be made to work with the liquid Alox base.

Feel free to PM me as you go along.

[BOOM BOOM]

HI,
I am glad you posted. I too love the 7MM bore.
I have abuot a 1/2 doz. low vel. loads w/ the 168 gr. gc lyman bore rider design for the 7mm/06.
I am currently experimenting to get a load w/ IMR 4198 near 1900,/s in the 7mm/06.
I also have about a 1/2 doz. low vel. loads 1200-1500'/s for my 7MM MAG.
I'd be very interested in hearing about anyones work with higher vel. loads.

[BOOM BOOM]

HI,
I have been using the Lyman #287308 168gr. gc. ,I believe it is what is being called a bore rider design. I have always leaned towards the heavier bullet designs as they could be possibly used for hunting & because of the velocity limitations of lead. The heavy bullets seemed to be the best bang for the buck.