Which cal to go with?
- Thread starter Chad280
- Start date
for my two 280ai, rem action, hart bbl, I took the path in load development this wqy,
fire a std 280 load to get a fired case, check the water volume carefully and compare as % of listed water volume for std case, mine was 1.074% so I took the std max loads of 4350 and 4831 upped them 3% and began ladder test,
my loads maxed out at +8% gave 140 3230fps but the accuracy node was +6.5% at 3125fps, the 160 gave similar increase and accuracy for both was well under 1/2 inch ,
you will love it, the cases seem to last forever. function in mag flawlessly. never looked back
Bob
fire a std 280 load to get a fired case, check the water volume carefully and compare as % of listed water volume for std case, mine was 1.074% so I took the std max loads of 4350 and 4831 upped them 3% and began ladder test,
my loads maxed out at +8% gave 140 3230fps but the accuracy node was +6.5% at 3125fps, the 160 gave similar increase and accuracy for both was well under 1/2 inch ,
you will love it, the cases seem to last forever. function in mag flawlessly. never looked back
Bob
Chad, I believe that is an excellent choice. I have 4 different 7mm's. If there is another for me it will be the 280AI. 3 out of the 4 I have the brass is very hard to come by.
Don Dunlap
I got lots of load data for 180gr bullets. .160 freebore is real good for 160-180gr bullets
This is a "possible" yes answer>>>BUT it is MUCH more than that.. Freebore is the length to the lands. The LONGER the bullet for caliber, the more freebore you need IF you want the bearing surface of your bullet to be above the neck shoulder junction, where doughnuts form. This is an area that has many variables. If you have a magazine well and are using cartridges designed for that action length, you may be limited in just how far you can set the bullet out and still fit in the magazine. Additionally, many, if not most competitive shooting disciplines, use a "single load" action. This will allow you as much or as little freebore as you wish.
Also, bullets have varying lengths of bearing surface, which would effect how much freebore is necessary to get that bearing surface past the neck / shoulder junction.. Another facet is how long is your case neck of the cartridge you are using. EXAMPLE: I have a .30-06A.I. and use 210 JLK's. My freebore is .125.. My shooting buddies who use a .308 for F-T/R use 210 JLK's BUT because the neck length on the .308 is MUCH shorter, they need a .270 freebore in order to accomplish what I do with less than 1/2 of that.
I know what you're thinking>>>ALL THIS GUY DID WAS CONFUSE ME! I do understand that>>> so maybe someone a bit more eloquent than I, will chime in and simplify what I am trying to say..
Bullet "jump" to the lands is all about how far in you put the bullet in the case and how far it has to travel to reach the rifling. You can control the amount of jump during reloading.
"Freebore" is the space in the barrel between where the brass cartridge case ends and the rifling starts. It's essentially a small section of the barrel bore that has the rifling removed.... ie smoothbore before the bullet hits the rifling. This is set by the gunsmith when they cut the camber in the barrel.
How long that freebore is determines how far in/out of the brass case the bullet will be, when it's set at the proper "jump" distance from the rifling. Less freebore means the bullet is deeper in the case. More freebore means the bullet is farther out.
Too far in and you lose case capacity that could be used for powder. Too far in and the bullet might be seated below the neck shoulder junction, with the potential that "donuts" forming in the brass case cause interference problems as the case is fired multiple times. Too far out and you might not fit the bullet in the magazine due to overall length. Too far out and you might not have enough case neck to hold the bullet as the rifling in the throat of the barrel erodes (freebore gets longer) from being fired over 1-2k rounds.
The trick is, that the "right" amount of freebore for your application depends a lot on what bullet you are using. Short bullets require different freebore than long bullets. And if you want to shoot both, then you likely need to compromise.
Now is the time to make this decision (with the help of your gunsmith) since it's done at the time that you chamber your barrel.
"Freebore" is the space in the barrel between where the brass cartridge case ends and the rifling starts. It's essentially a small section of the barrel bore that has the rifling removed.... ie smoothbore before the bullet hits the rifling. This is set by the gunsmith when they cut the camber in the barrel.
How long that freebore is determines how far in/out of the brass case the bullet will be, when it's set at the proper "jump" distance from the rifling. Less freebore means the bullet is deeper in the case. More freebore means the bullet is farther out.
Too far in and you lose case capacity that could be used for powder. Too far in and the bullet might be seated below the neck shoulder junction, with the potential that "donuts" forming in the brass case cause interference problems as the case is fired multiple times. Too far out and you might not fit the bullet in the magazine due to overall length. Too far out and you might not have enough case neck to hold the bullet as the rifling in the throat of the barrel erodes (freebore gets longer) from being fired over 1-2k rounds.
The trick is, that the "right" amount of freebore for your application depends a lot on what bullet you are using. Short bullets require different freebore than long bullets. And if you want to shoot both, then you likely need to compromise.
Now is the time to make this decision (with the help of your gunsmith) since it's done at the time that you chamber your barrel.
Like said above freebore keeps the bullet out of the donut area. That is important. The pressure ring of a bullet should not be seated past the sized part of a neck. Usually if this happens, bullet grip and accuracy will be lost. Keeping the pressure ring in front of the neck shoulder junction helps reduce pressure and usually gives more velocity because you increase the volume of the case. Matt
MTlager
Silver $$ Contributor
Chad, I have 180 freebore on my reamer and it works well for the 160 Accubonds to the 180 Berger vld, and still have room in your Remy magazine. I wouldn't go any longer than that unless you were going to shoot the Berger 195's. The Nosler brass runs about .310 on loaded neck diameter, so go with a .314 or .315 neck on the reamer for a no turn neck.
Lonnie
Lonnie
All this stuff seems to be confusing to you chad 280. I understand as we didn't just aquire knowledge without experience in the loading field. Here's the facts... Both the 280 and 284 will be close in performance regardless which action you pick. The 7saum will be a bit faster. Here's the thing. The 284 seems to be the ticket at the 1000 yd line in competition. How many 280 guns do you hear of on that same 1000 yd line. This simply means that the 284 is a winner of a cartridge. Not saying the other 2 aren't fine options but tried and proven always wins over equal or greater speed. Seems that shorter fat cartridge has and is winning over the 280 and even the shorter 7saum. Just saying. Given the choice, I think it's clear for accuracy sake and ethically speaking on game the 284 is your solid choice. If it was a toss up, this may be your tie breaker.
Yes jump to the lands
I'm not sure if there is a Saami spec for how much freebore to use. I do believe that a smith can use the standard SAAMI reamer then use a separate tool to add additional freebore afterwards.
I'm not sure how compatible the freebore is between the 180 Hybrids and the 140 AB's. I can tell you that they are quite different in length, with the 180 Hybrid being 0.237" longer than the 140 AB.
Here's a couple pictures to help you visualize the issues we're talking about. This is my 280AI brass with Berger 180 Hybrid bullets. First picture just shows the possible bullet positions depending on how much freebore your chamber has. One has the bullet crammed down into the case.
The second picture has the 180 Hybrid laid alongside so you can imagine what's going on inside the case.
The key factors we are trying to get when choosing a freebore are:
1) The bearing surface of the bullet is above the case neck junction.
This optimizes case capacity, ie more room for gunpowder. This also avoids potential intereference on the bullet from "donuts" forming. What's a donut? It's when the brass in the case moves from repeated firings and creates a "pinch point" that prevents a bullet from fitting in the case anymore. Tough problem to deal with and annoying. FWIW, I haven't gotten any donuts in my 280AI using Remington brass and I'm currently on 7-8 firings.
2) You are able to reach out and touch the rifling with the ogive of the bullet.
Some bullets shoot best when just slightly into the rifling or when jumping just a short amount. Being able to have this as an option is a good thing for accuracy tuning.
3) There is enough bearing surface left in the neck in order for the case to hang onto the bullet.
This could be a problem if you had a very long freebore and then tried to seat a short bullet all the way out to touch the rifling. It might be too far to stay in the case. The simplest way to do this is to seat the shorter bullet normally and let it "jump" to the rifling.
My recommendation would be to choose your target/accuracy round and build the gun around those specs. Then for hunting season you can just shoot the shorter bullets with a bit of jump. As an aside, pretty much all factory Remington 700's have a really long freebore so pretty much all bullets have to jump.
Thank you! That's what I was thinking. My smith is very good. I have told him the bullets I am primarily going to use so he is gonna build it around it. I would like to get 3 of the eld-x bullets and make three dummy rounds for him to set it by. Just can't find any damn bullets!
Again thank you all for your help and explanations.
Again thank you all for your help and explanations.
I found a good accuracy node at 2820fps using 59.8g of H1000 with a COAL at 3.643". I haven't bothered going higher than that since I don't want to beat up the brass and reduce case life. Using Quickload software as an estimating tool, my load is only at 53k PSI for pressure and I could theoretically go up to around a 63g charge weight with velocity up around 2950fps from a 25.5" barrel at 65k PSI. I don't have any pressure signs now and haven't worked up to the point where I've seen any, so I can't say for certain that would be possible.
Current velocity gets me to almost 1 mile supersonic at my shooting altitude, so I just figured I'd stick with accuracy and not chase velocity.
Current velocity gets me to almost 1 mile supersonic at my shooting altitude, so I just figured I'd stick with accuracy and not chase velocity.
280AI will do fine. Look at the 7 Rem Mag vs the 280AI. Not a lot of difference in velocity; and when you run the numbers out to 1,000 yards, the difference is minimal. You did the right thing. I would go with the new tipped bullet, ELD-X, or whatever it's called.
Upgrades & Donations
This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.